really only do it if its small white crystals or small brown rocks, if you get it in powder form there is a good chance that it is cut. the brown rocks do crush up into a white powder so it doesn't neccisarrily mean its cut, but personally i will never by powder again from to many bad expirences. also if your mouth gets numb when you eat it, then it is cut with either coke or meth.
besides that remember to drink water while your on it, especially since your going to a concert and will probably be dancing. but limit yourself to like a bottle of water an hour. the biggest cause of death on mdma is from dehydration and hypohydration. so if you drink a couple of bottles of water you should be fine
also gum is very important!!!! you will be grinding your teeth alot. i recomend orange swirl trident splash because not only it has the amazing taste of orage sherbert, but it also has liquid in it that explodes in you moth when you bite into it.
besides that, you really have nothing to be worried about.