Don’t worry… it is almost certainly just the newness of the situation. If I read your post correctly you have only had sex 4 times total in your life, correct? Any new situation has anxiety attacted. Very normal. I am also assuming that you can achieve orgasm through masterbation. If you can not, that is not normal and a trip to a Doctor (endocrinologist) may be a good idea. Assuming you can ejaculate through masterbation… stop worring.
Remember, the woman is often ALSO worried… woman VERY typically worry about things like, “does he think I’m pretty?”, “are my boobs big enough/pretty enough?”, “does he think my butt is big?”, “do I smell funny?”… and on and on and on. So, to be a good lover you just want to be attentive and LOVING! Do that and the rest is insignificant.
Again, don’t worry about HOW you feel. Just get into the woman mentally, focus your thoughts on what you like best about her. Personally, I love kissing a woman deeply and in fact sometimes have to avoid doing so if I want to stave off coming. Again, stop thinking about your body and your performance and instead think of her body/mind/sexiness and nature will take care of itself.
Remember, it is completely unimportant that you come or not. After all, you aren’t TRYING to get her pregnant.
PS, if you don’t come, DON”T tell her… she will probably take it as a sign that you don’t like HER!!! Just tell her it was wonderful REGARDLESS. If she asks, tell her YES regardless. Notice a trend here, a woman is a fragile being and is very vunerable when it comes to sex. Now, I am not saying lie on a long term basis, but when a relationship is new it is a good idea to avoid injecting anxiety into her mind.