loosing my virginity

I'm 16 years old and I have been going out with my boyfriend for nearly 2 years. we have been wanting to loose out virginities to each other and we have been trying but it seems that his penis doesn't fit in my vagina and I want to know why but no one can tell me. any tips? I just want to share this special moment with him. I want it and so does he, it's just another step in our relationship that we want to go through together.