Last night, I had this kind of experience.

Then last night, {the last night on| the lastend} of the Chinese New Year holiday, I {just found | suddenly realized} that I hadn't done it.

So I immediately grabbed my phone and edicreated a video about one of my Niaoxiaohua -- a dahlia immediately.

It’s possible to keep “immediately” at the end of the sentence, but then you’d need to add another long dash: “…about one of my Nianxiaohua -- a dahlia -- immediately.”

I don’t think “edited” works well in this context, since you had to do much more than edit a single video clip: you recorded several clips, combined them, added voiceover, captions & subtitles, etc. “Created” works well instead.

I'll show you in a week -- at least I hope so.

“At” should not be capitalized.

Have you ever had a similar experience?d this:

"Have you ever had a similar experience" is a phrase I would use after discussing the situation. So you start the conversation asking if the reader has experienced something I would format it as "Have you ever experienced this:".

The new term is about to start, but you haven't finished all your homework yet.?

Might be more of my own opinion, but I'd add a "?" here as you are generally asking a question!

Last night.

Then last night, the night on the last of the Chinese New Year holiday, I just found that I hadn't done it.

Sentence is correct, but another way to phrase it could be "last of the Chinese New Year holiday, I just realized that I hadn't done it."