Virginity?!

ok so this is gonna sound weird but this is the only way I can relate. When you loose your virginity or in fact if you have sex in general I'm scared for his penis to actually go in, like when you are putting a tampon and sometimes you struggle to put it on because your muscles tension up does that often happen during sex?im scared in case it just won't go in but then I'm also thinking, the penis is that big will it just start going in itself?c