At least it was your car on your time.
Worked with a guy at a dealership who swapped a 3800 in a FWD C/H Body Buick.
Buttoned everything up top, raised car for bottom work and.....no flex plate.
Happens to the best of us.
I always say there are 2 kinds of people who don't make mistakes:
-those who don't do anything
-liars