Going over the ground rules with everyone involved is crucial and if you don't go over the rules this is what will happen. One problem I first saw was that you admitted that both of you were half buzzed, bad idea. Next, are you sure she was an anal virgin, maybe she has done it before? Anyway it happened, now what to do about it. I think both should stop until you both get on the same page with your rules. This is not uncommon, I have really seen problems about going bareback or ejaculating inside her. Having rules and sticking to them is important and later down the road you may adjust your rules. Talk this out and don't let this get between you, but don't swap until your rules are agreed upon by both!