Looks like cigroller got you going in the right direction and you’re not an idiot for making a mistake. On the contrary, you were astute enough to go back and find the problem whereas many people might have wrestled it for weeks before throwing in the towel and having the car towed to a shop or worse; maybe even scrapping the car.
(I had a guy bring a small block Chevy in once in which he had pulled the engine and removed the cylinder heads on the assumption that the motor was running poorly because of a compression problem. The cause? Two bad plug wires. Ouch.)
Everyone makes mistakes now and then, even mechanics, and any mechanic who says he hasn’t is lying through his teeth. I’ve made a few but thankfully nothing major in scope other than an embarassing one to this day error I made about 10 years back. Memory just won’t let that one die. 