I have never had problems with it. And i have taken 2 very thick ones. When i think of them now, i just don't understand. I was virgin too!!! The thing is that i accepted to take them.
A foreplay has its effect too.
Let him eat your ass for a long time, and you'll want him to enter you. That hole is going to want him into you naturally.
But you have to know that once it's done and he starts fucking you is not everything.
Every time i got fucked, i appreciated it at the begining, but 3 or 4 minutes after, it wasn't good for me anymore. So i always asked to stop. Yeah deceiving for my partner...
So you have to listen yourself and no matter the size, if you want it in you, you'll take it very easy, otherwise, since you decided in your head that you don't want it anymore, it won't be good for you.