Women seem to very a lot in vaginal depth and whether they like to be pentrated to the full depth of their vaginas, in my experience.
I am a little over 7 inches long and between 5 1/2 and 6 inches circumference, which I reckon to be above-average, but not "big" and certainly not huge.
Out of maybe two dozen partners, I have "bottomed out" in a little over half, and not in all positions, even then. I have been considered a little large for comfort by about one in three, to the point that I had to exercise some caution and restraint to avoid causing pain with vaginal intercourse.
Most of the women I have been able to hit "rock bottom" with did not like cervical contact. One or two did, but only when very aroused, and then it seemed to be a "pleasure-pain" thing.
What does seem to work for most, is to slide behind and past the cervix to the "posterior fornix" or cul-de-sac, which is the deepest part of the vagina. You need to go gently at first until the uterus and cervix get out of the way and the vagina elongates, and you may need to adjust position and/or angle to get there. For me cowgirl, or woman-on-top seems to work best. You may need to forgo vigorous in-and-out thrusting, and just stay parked and do a lot of pelvic rocking and grinding (which allows more clitoral stimulation anyway), but this seems to work pretty well for a lot of gals, and is likely to give you more staying power.
dude there is no need to worry about that mines even a lot smaller then that and it really doesnt matter so what if you couldnt do it with your dick you ca do so many more things to please your girl but im sure a guy of your size ca definitely do it me on the other hand no but hey thats why i try other things