You need to slow down a bit here.
There are different measures, in different cultures, to determine whether a woman is a virgin. Believe it or not, in some cultures a woman who is not a virgin is not as worthy as one who is.
I am assuming you are somewhere in Canada or the USA. Assuming that, I would say the worst thing you did was TRY to have sex, and sex wasn't possible because you were not ready, and it was painful.
Does that set your mind at ease at all?
If that is all you have done, stop beating yourself up over it. Had the 'lie' included multiple partners, a couple of kids, and a few STD's, that would be a red light for anybody.
But all you did was say you were a virgin, and I think you can safely say (without a medical or moral judgment) that you are a virgin. The beginning of sex happened yes, but if that were to be judged even as a consummation of a marriage, I'm not sure it would count because it wasn't completed.
Anyway, just my opinion, and but asking someone if they are a virgin should be off limits, and none of your business in the first place. That can open up a whole can of worms. And anybody asking you the same question, should be flatly told it is none of their business.
And, the relationship is only 4 months old! Learn as much as you can about your boyfriend, know him as a friend, whether you can trust him or not, is he honest, reliable, etc. etc.- the important things to know and be sure of, before you have sex with him. (and finish what you started!)