Tight Vagina - Please Please Help!

Ok, so, the entrance to my vagina (which is like a ring of tougher skin, as it should be) will not stretch. The insides are fine, I can fit two fingers up there easily but whenever I try to use a dildo it feels like it's about to tear, and i literally cannot use any more lube. My dildo is 3.75" in girth, so less than the average penis. I am a sort of virgin, tried it once and his penis didn't go in which at the time was assumed because he was drunk but now I'm not sure. It's not a hymen issue, and it's not vaginisus, it's just that the entrance literally will not stretch any further, and I'm scared for what this means when I do have a proper sexual relationship. Has anyone else had this problem, and if so, what was the solution?