I very much doubt one drink will have any lasting effects. You may well feel bad for a week or so, but I don't see any mechanism whereby a short exposure to alcohol could erase all the progress you made. So, not repeating the experiment would be the best bet, but I think you already know that.

Try not to stress about it too much either, as that would only make things worse (the effect stress has on my PN is staggering). You tried, it didn't work out, dust off and keep going.