I'm sorry you feel so down about your birthday
If it helps, I too have been there before, as my birthday is at a really inconvenient time.
That's no reason to sit at home though! Get out and have fun. Even if a lot of people aren't there and you decide to not do karaoke, you shouldn't spend it at home. Speaking from experience, it only contributes to making you feel worse. Plus, you have the lovely convention to make even more friends!
Hang in there sugarlat and have a happy birthday <3 <3 <3