Is it big enough? I don't know. I'm not your girl. Do you stay hard long enough? I don't know. I'm not your girl. But whatever the the size, you'll have to make it enough. You'll have to pay attention to your lover to see what she's feeling, and respond to her desires, just as she'll be responsible for making sure you know what those are, and for seeing to yours. If you stress yourself out beforehand, over-thinking every detail, expecting absolute perfection, you're going to have a terrible time. Remember that one reason you two are having sex is that you have great chemistry. You make each other horny. Maybe there are other reasons too (I don't want to assume) and none of these have terribly much to do with the size of your penis.