Ex won't stick to custody schedule and I'm losing it

So my ex has been picking up our kids (7 and 9) whenever she feels like it, completely ignoring the Wednesday/Friday schedule we agreed on. Last week she grabbed them on a Tuesday without asking, and I had already made dinner plans. Then she keeps them an extra day 'because they want to stay.' I'm not trying to be a jerk about this but like... I plan my whole week around my custody time. How do you guys handle this without turning into the bad guy? Do I need to get a lawyer involved or should I try talking to her again?