Find out what turns your girlfriend on, and then follow that path, the woman needs to get excited to cause her vaginal vault to tent upward away from the labia lip opening, this will also cause her to become moist and well lubricated, another thing you can do as it was mentioned before is use your fingers to stretch, but also allow her to relax on taking width, one finger and then two fingers, you may even get to 3 fingers, let her help you too, she may guy your fingers by reaching down and pressing on your elbow or grabbing your wrist and adding pressure to insert further or harder....You could also allow her to be on top and control the entry of your penis, but a word of warning, your penis can be damaged if she gets to aggressive and presses to hard, you could actually sprain your dick, basically it creates a wicked bend and then their is a snap and pain follows, use your hand to support you penis by grabbing it so she can push down hard without hurting you. Eventually she will be able to take you....The first time my wife and I had sex she could get me in but the head, and about bend my dick in two, so from experience it takes multiple attempts, lube, and your woman to relax....Hope the best for you....