I recommend that you first have a good look at your hymen and see if you have any left. You can do this by holding a mirror between your thighs and look or you can go to a gynaecologist for a brief exam. If you Google Hymen and then look at images it should give you an idea what to look for. I doubt that you still have a lot left because most women lose their hymen due to physical activities, tampon use, etc. in very rare cases it is still in place and tough to break but this is very RARE. That’s why I say check yourself first to have an idea as what the opening of your vagina looks like and be reassured that it could open up to accommodate any penis size. There are many horror stories out there about the first time but they are often not true and made up to kill your appetite for sex.
I would also recommend that you make sure to prepare well (have condoms, be with someone that you trust and feel is the right one for you, you are having sex for the right reasons not because you are drunk and can’t push back). Studies show women might regret their first sexual encounter if not prepared for it emotionally and physically.
By the way one of the most common issues with the first timers (boys or girls) is disappointment because the way sex is portrayed in our minds is a mind-shattering, life altering event which is not even close to the real experience specially the first time (because it takes time to learn how to really enjoy it an become harmonious with your partner) so don’t be discouraged. Just relax and enjoy the experience that is the best way to go about it.