Thank you all for your sympathies. (Though some of you missed my sarcasm). I know to measure twice and cut once. I had intended to cut a tee shirt 14" wide and 16" tall and got it reversed. Instead of tall and skinny it is short and fat. Oh well, I can (and did) fix it. Just a tad frustrated with myself.
I use the InvisiGrip on the back of my rulers and it helps reduce the slippage. Maybe that hint will help someone else.