I was on the patch for about a year, too, and sometimes changed it late. I didn't use a back-up method all the time, either and I didn't get pregnant. I hope this helps to put your mind at ease. Ashelen is right, stress can make you feel pregnant sometimes.
You're most likely fine...I've gotten pregnant while using the pill before, but I used the patch for about 3 years without any back-up and never got pregnant. If your period is very late I would take an HPT but if you stress about it too much you could delay it, so just try not to worry. You can always use the Plan B as long as you use it fairly soon...I think it has to be before 48-72 hours after the intercourse but I'm not sure as I've never used it. I would say just continue with the patch and condoms combined and you should be fine in the future, but its a very low possibility with the patch even if you put it on a few hours late. I NEVER put mine on at the same time on change day and it worked fine for me. Just continue to be careful and try not to stress :).