+ vote for what stutyr says, Alex. Doing a last long run 3 weeks out is what's recommended by many. Ideally, yes, you would have logged a couple more, but you will not gain additional benefit by doing so now - you'll just dig a deeper hole to recover from.
Going out and doing a half marathon, many, many people basically overperform on the day, surprise themselves with how well they've done -- and take a while to fully recover afterwards - and that's absolutely fine. You've done a ten and that's very close to your target distance - remember that and remind yourself whenever you have any doubts.
Follow your taper plan, stay focussed on all that you've achieved, get the right nutriton and sleep and you'll be fine.