Well, you seem like a considerate enough lover. At least you came here for advice first, so kudos for that. I'm assuming its not some stupid post-teen bragging thing. Taking someone's V is no big deal. Someone has to do it and at least you sound like you care her experience isn't a poor one. Just be gentle on her emotionally b/c its a bigger deal for gals than guys. I certainly hope you aren't planning on dumping her anytime soon and even maybe considering something long term.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh