Although I don’t have OCD, I have ADHD. Your condition causes you to have anxiety about it, and my condition makes me more likely to actually do one of those things :)

How I’ve gotten around the anxiety (as I actually have left doors unlocked to my detriment on multiple occasions, have left the stove on etc.), is I say it out loud as I’m doing it. “Locking the front door.” Sometimes I might have to add a day: “Monday morning. Locking the front door.” as my brain will occasionally trick me into thinking that memory wasn’t from today.

I did this enough that now it’s somehow ingrained in my head and I don’t forget to do things as often. I’m not sure if this would work for you, but it might help.