Hi, I feel you. In my case, a project that was supposed to take 2 months, Took nearly a year to complete. By the time I completed it I almost couldn't stand it. It is not a case of not being a better me/you.
That is just the nature of the beast. Each software project/business is unique. So it is impossible to make accurate estimates. New features will keep cropping up. An integration that was supposed to be straight forward would fail because library A does not play well with library B. To hold yourself responsible for something beyond your control will obviously hurt you.
This is just an experience for you to learn that feature creep is real. Working alone is different from working in a team. In a team, gathering requirements, making estimates, development, marketing, sales, support are each shouldered by different teams. Each team would have multiple people. So any individual ends up with a small share of the responsibility pie. They have the luxury to draw a line on how much stress they would like to handle or move out.
In a single person company, one person gets to handle all the responsibilities and there is no way out short of giving up. The way you manage it is entirely different and that is what you really learn the first time you start a company. It took me nearly 3 projects to understand this. This is the rite of passage for Everyone who goes the solo route because there is nothing in the corporate/employee world to prep us for this.
Nowadays, I try to keep the features as minimal as possible. Everytime I ask, is this truly needed for the first release. I go to local meetups when ever possible to be among like minded techs.
Happy Producing.