Doggy style struggles

So my fwb and I recently were experimenting with doggy style and it was such a struggle to get him in and especially keep him in. He kept saying that my vagina is really tight, could that actually be the issue? His penis isn't super big either so I'm not sure if that is the problem. We tried on hands and knees on the bed (my upper body was completely on the bed with my butt up in the air) and then we tried me laying with my legs off the side of the bed and him standing but neither seemed to work super well.