First Time , help needed?

Alright, well I'm currently 16 and I've been dating my girlfriend for three months now. We have mutually decided that it is time to have . We are both virgins. We have done many other things, so we both feel ready. Yesterday, in the heat of the moment, she said she wanted to have , so I made sure she was completely sure about it and she said yes. So I slipped on the condom and what not. Being that we had fooled around for a while she was extremely wet, so I felt that was all the lubricant we needed. Also, just to let you know I'm over a foot taller than her... me being 6 1 and she being 5 feet. So I wasn't entirely surprised that she was really tight. However, I didn't expect her to be so tight I could barely enter. And it's not like my is ridiculously huge. It is around 6 inches, average. Back to the story. After around 3 minutes of trying to enter and her facing a lot of pain, we decided to forgo this activity. It was almost virtually impossible to enter 'cause she was soooo tight. Also, the fact that I'm so much taller than her made it quite awkward for because of the height difference. We are planing on trying to have tomorrow, after I buy lubricant 'cause that would probably help out the . So I wanna know if this is a very common occurence and any tips on how to make this go smoother. Much appreciated.