>>76300710Cardio is your biggest factor. If you dont have that the rest wont matter. As a virgin there is a good chance you will be a 2 pump chump. No shame in that, you will be ready to go again soon.
But cardio is the most important aspect. Gets you harder and you can fuck longer.
Next would probably be core, when you are on the bottom "bridging" hits the girl really hard. By bridging i mean just pushing up enough that she isnt pushing you into the matress.
Besides those i dont really think any muscle group will matter more than the other except for very specific stuff like arms for fucking her against the wall etc. But don't sweat that kind of stuff at first.