I wouldn't worry too much about it, tbh. You've had a good 2 weeks and then had a slip up, which is hardly that bad anyway as it's fruit, which is okay in moderation. I'm not sure about how far it'd set you back biologically, would probably be too many variables to give an accurate figure. I'm a big fan of averages myself. So if you gorge on a load of fruit that equates to, say, 150g carbs, in 2 weeks that's added about 10g of carbs to your daily total. No big deal. You certainly haven't undone 2 weeks of effort in one evening.
I'd be more worried about dipping celery in peanut butter though. Not because they're particularly bad foods either, just that it sounds like a horrible combination!
The bigger problem is probably how you feel about it mentally. DO NOT start beating yourself up about it. Pointless and counter-productive. We all slip up from time to time, even those hardcore few who claim to be 100%ers. I'm a devout foodie and will partake in small amounts of very un-primal foods from time to time. It fits into my 80/20 and, you know, life's for living. If your only slip is a 2-weeky fruit session and a bit of peanut butter, you're doing great.