you have a choice - you need to accept that its over and done with now and you cant take it back, but you can either feel bad about it or you can feel positive that although you have had a bad day, you will stick things out and see WW through until next WI and beyond.
We all have bad / off days but its not the biggest deal in the world so dont worry yourself too much over it
if you can / want to, save 4 points each day until WI and that will at least limit the damage you have done slightly xxx
treating yourself is fine but its always best within points if you can as for the others - there are plenty of people out there who will see you losing weight and although their intentions are sometimes good (mostly theyre not..) they often lead to sabotage of your good efforts!
however important thing is, if you enjoyed yourself thats all that matters - you have a lifetime to lose weight, so you cant deny yourself a good time x