I would pull each of your headings up a level so you can take lessons into the future:

I built the entire thing before ever announcing it = I didn't talk to customers.

I built a huge feature for my only customer = I didn't have a vision.

I wasted too much money on AdWords and Fiverr = I had no marketing plan.

"If it had @thisAmazingFeature, then I would buy it" = I didn't stick to my vision (because I didn't have a vision to stick to).

Most importantly, I can't relate to my target demographic at all = I don't care about the project.

A plan of action = What I should have had in the first place ;)