My girlfriend ate the food I had saved for three days, so I cancelled our dinner plans

I had a container of my mum's lasagne in the fridge with my name on a sticky note. I'd been looking forward to it all week. I came home and the container was in the sink. She said she "didn't think I'd mind". I told her I wasn't in the mood for our dinner reservation anymore and stayed in. She says I'm being childish over pasta. Am I overreacting?