Not sure if I'm reading this right. You've been just friends for the past 2 years and now you're in a exclusive relationship? Am I getting it right?
Anyway... saving yourself for someone you love, to me, seems like a lie you tell yourself to feel better for not ever having sex yet. If I'm right, you may as well admit it. Not to me, or to the forum, but to yourself. It's not really
that big of a deal anyway. If I'm wrong, well, more power to you.
Best advice I can give you is to not think about it 10 times / hour for the next 24 hours. You know what happens when you over-think stuff. Groom yourself, make yourself desirable and stop worrying about silly shit like "is my dick big enough". You got this. Take control.
As far as actual sex goes...well, you only get good at having sex by having sex. Sure you can read up some guidelines on how to please a woman, but please keep in mind they are just that - guidelines. Use those as you see fit but don't be stuck up in your own head. Don't do what 80% of guys do and immediately jump on her ass / tits and remain there for the entire duration of the act itself. Take your time, women like men who pay attention to their entire body, not men who forget themselves in one specific area.
Most importantly, pay close attention to her body language and reactions. Those will tell you more about what / how she likes than a million guides or videos will.
If there's anything else, please say so. I want to help you out in any way I can

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