what if I'm too tight??

So I am going to this boys house this weekend to stay over, we have previously done stuff and we've been like this for 5 months, we've never been alone alone, our only times together being music festivals in EaChothers tents and parties. We've both never had sex before and we are pretty certain we are going to this weekend, we joke about it a lot, we are so attracted physically. What if I'm too tight? I'm 18