I (23M) lied to my GF (21F) about being a virgin and dug myself in a hole

I’ve been seeing this girl for about a month and a half now and things are going great. On our first date, she told me she was a virgin. For some reason, I totally panicked in the moment. Instead of being honest, I told her I lost mine at 17. Since then, I’ve just kept digging the hole deeper. She asked about my past relationship and I told her I’d been with my ex for 7 months and we’d had sex dozens of times. I later said again I wasn't lying when she asked about it later.

The ex and I never actually had sex because I just didn't feel ready at the time. I think I’ve just been really insecure about being 23 and having zero experience, so I made up a fake history so I wouldn't look weird.
We haven’t had sex yet. And she is really bummed not being able to lose her virginity to another virgin. I feel like a total asshole for lying to her face. I don’t want our relationship to be built on this, and I feel like I need to tell her before we actually end up sleeping together.
I’m terrified that the fact I lied so much (and swore on it) is going to make her break up with me on the spot.
How do I even start this conversation? Is there any way to come back from this?