3 Days Trip

You're right that we normally use the plural "-s" form of a word after a number over 1, however this context is a little different. Basically, when you are modifying a noun with a number and another noun, that first noun is singular. Here are some examples:

"3 days" but "3 day trip"
"5 people" but "5 person family"
"2 beds" but "2 bed room"

A man who I met at the event teach me about anold me that another event in Kanagawa prefecture would be held next day.

I wander if I should go butthought about it, and I decided to go there.

After I come back home in Aichi Prefecture late in the evening on January 7th, I reserved a hotel for the next day, and I left for Kanagawa prefecture early in the morning on January 8th.

I attended the event and then I had a dinner with the man who teachold me about the event and his friends, and talked about a lot of things.

I enjoyed it very wellmuch.

On January 9th, I went around Kanagawa prefecture for a while, and coame back home in Aichi prefecture.

It was quite a big trip for me, so I thought about myself asit made me feel like a person who had the power to take action.

A 3 Days Trip

On January 7th I went to an event in Hyougo prefecture on January 7th.

A man who I met at the event teachold me about an another event in Kanagawa prefecture that would be held the next day.

I waonder if I should go but I decided to go thereed whether to go or not and decided I would.

After I coame back home into Aichi Prefecture late in the evening on January 7th, I reserved a hotel for the next day, and. I left for Kanagawa prefecture early in the morning on January 8th.

I attended the event then I had a dinner with the man who teachhad told me about the evenit and his friends, and talked about a lot of things.

I enjoyed it very wellmuch.

On January 9th, I went around Kanagawa prefecture for a while, and cothen came back home into Aichi prefecture.

It was quite a big trip for me, so I thought about myself as a person who had the power to take and I was pleased with myself for being so proactionve.

3A Three Days Trip

A man whom I met at the event teachold me about an another event in Kanagawa prefecture that would be held the next day.

I waonder ifed whether I should go but, in the end, I decided to go there.

After I come back home into Aichi Prefecture late in the evening on January 7th, I reserved a hotel for the next day, and then I left for Kanagawa prefecture early in the morning on January 8th.

急がそうでしたね。

I attended the event and then I had a dinner with the man, who teachold me about the event, and his friends, and we talked about a lot of things.

I enjoyed it very wellmuch.

On January 9th, I went around Kanagawa prefecture for a while, and then coame back home into Aichi prefecture.

3 DThree-days Trip

reference for "three-day": https://thegrammarexchange.infopop.cc/topic/three-day-trip-or-three-days-trip; the second element of a hyphenated word isn't capitalized in a title

A man who I met at the event teachold me about an another event in Kanagawa prefecturethat would be held the next day in Kanagawa prefecture.

Although I decided to attend, I wandered if I should go but I decided to go there.or not.

when you use "but" here, it seems like the sentence wants to take a negative turn - as in, you decided not to attend.

After I come back home into Aichi Prefecture later that evening on January 7th, I reserved a hotel for the next day, andother event. I left for Kanagawa prefecture early in the morning on January 8ththe next day.

I attended the event t. Then I had a dinner with the man who teachold me about the event andlong with his friends, and we talked about a lot of things.

I enjoyed very wellvery much enjoyed the night.

a little awkward in wording

On January 9th, I went around Kanagawa prefecture for a while, and coame back home into Aichi prefecture.

It was quite a big trip for me, so I thought about myself as a person who had the power to take action.

Awesome :)!

A 3 Days Trip

A man who I met at the event teach me about aninformed me of another event in Kanagawa prefecture that would be held nextthe following day.

I waondered if I should go butor not, and in the end I decided to go there.

After I coame back home into Aichi Prefecture late evening on January 7th, I reserved a hotel for the next day, and I left for Kanagawa prefecture early in the morning on January 8th.

I attended the event then I had a dinner with the same man who teachold me about the event and his friends, and we ended up talkeding about a lot of different things.

I enjoyed very wellit thoroughly.

On January 9th, I went arounexplored Kanagawa prefecture for a while, and come, and then went back home into Aichi prefecture.

It was quite a big trip for me, so I thought aboutnow think of myself as a person who hads the power to take action, and to be independent.