I know this feeling man, and it will really help if you have a prepared answer for this.
So write down all the questions you're worried about hearing, and all the follow up questions, and develop answers for them. Even better, form an opinion for yourself that frames your actions as alpha, then you can get hit by any question and you have your opinion to back you up.
For example you can have this opinion: I'm very picky and only date girls that are smart, can sing, athletic, whatever...so I haven't dated that many girls...but i have had A LOT of fun

(evil laugh)
and if she still asks, "what fun?" or "so how many girls have you dated" just frame flip her ass and say something like, "I'll leave it up to your imagination," or "that's such a weird question to ask...i don't count, haha"
Frame it in your head first, adopt that frame, believe it; then you can be the guy who's only been with one girl but has the confidence of and above average guy
Also do drills! get your buddies to shit test you and ask you questions then hit them back with your answers.
Good luck with this dude.
Everfresh