See above for my corrections and comments in red.Hi,
Could you please correct these sentences?
1- The most valuable thing I've ever had was a 90-meter square apartment that I won in a lottery. (Is it possible to use lottery here or is the lottery only used for money?)
Yes, you can use "lottery" It just means a competition where you buy a ticket or choose numbers and then someone wins.
The phrase "90-meter square apartment" doesn't work. That sounds like a square apartment which somehow measures 90 meters. It's either a "ninety square meter apartment" or a "ninety meters squared apartment". I'm not sure which one applies to apartment sizes because we don't measure our accommodation in the same way in the UK.
2- I had a 3-year-old daughter who needed to be looked after 24/7.
3- One day, I heard about a house lottery taking place in our company.
4- I registered my name disappointingly cause I could have never imagined that I'd win. (Is the tense correct?)
Firstly, you didn't register your name "disappointingly". You might have registered it reluctantly (if you didn't really want to) or pessimistically (which fits better).
For the end of the sentence, I would use "I could never have imagined [that] I would win" or "I never imagined [that] I would win".
5- It took two years until the building of these apartments had finished.
It's OK but a little unnatural.
It took two years for the building of these apartments to be finished.
These apartments took two years to build.
6- Can we say "attend" the lottery? (e.g. There were four people attending the lottery.)
No. People "take part in" or "participate in" a lottery. They might attend a lottery draw, the event where the winner is chosen.
Thank you in advance.