Ex not following custody schedule and I'm losing it

Court order says she has kids Wed night through Fri morning. Last month she picked them up late 6 times and dropped them off early 4 times. When I bring it up she says I'm being rigid and the kids want to stay longer. Yeah they do want to stay with their mom, but that's not the point. We agreed to a schedule for a reason. Do I need to lawyer up again or am I overreacting?