Elimination diet: Did I mess it up?

Hey, I'm doing an elimination diet of gluten, dairy, and eggs to see if I am allergic to them. I know you're supposed to be free from any of that for 4-6 weeks, and I've been doing it for 2 so far. Last night I ate movie popcorn as they said there was no dairy in it, and didn't think there was gluten. I got it without butter, but they said its cooked in some buttersalt oil that has no milk products in it. I'm wondering now if it had gluten in it, or maybe my body is just used to eating healthy and didnt like the preservatives in the root beer or popcorn oil? Anyway I ended up getting sick and am wondering if that was to blame. If it was (I'll call tonight and hopefully find out from a manager), do I need to start the elimination diet all over again? Like have 6 weeks from today rather than just 4 weeks left? I know it's just to get any traces of the foods out of your system so you can really see how it effects your body, but I'm just not sure yet (after 6 weeks I start adding those foods back in slowly and see how it affects me). If anyone has any knowledge on that or has done an elimination diet themselves, any information would be helpful. Thanks!