I haveneed to submit a thesis for my training, so I worked overtime.raining report, so I stayed late at work. I need to submit a training report, so I stayed late at work.

Instead of 'thesis' use report for a layman to understand.

After work, I went to the supermarket and then cooked for myself. After work, I went to the supermarket and then cooked for myself.

After work, I went to the supermarket and cooked. When I got home, I cooked dinner for myself. After work, I went to the supermarket. When I got home, I cooked dinner for myself.

U didn't tell us where you cooked dinner...I presume you cooked it at home

I also had watermelon. I also had watermelon.

I hadalso ate some watermelon. I also ate some watermelon.

Using the verb ate helps to describe the action

They’re good.It was sweet and refreshing! It was sweet and refreshing!

Describing the fruit taste is good because it well explains how you felt after eating it.

I hope tomorrow will be a good day!

Today is my second diary entry. Today is my second diary entry.

Today is my second diary. entry. Today is my second diary entry.

It's your diary so, a possessive noun should be attached "My".. Entry should also be attached because you're writing to tell us how your day went.