Sure, social anxiety might be part of the reason. But I think the biggest contributor to your lack of success was that you did not have a team around you to build the product. With a team, I'm sure you would have found it much more acceptable to cold email people and just feel no shame basically promoting the product.
But that's one part of the whole picture. Sometimes, I guess, you just have to admit that people don't want to buy your product. Maybe it's because you don't know how to market it or maybe it just doesn't provide that much value.
I wish José best of luck to future endeavors and I recommend getting to know other start-up oriented people. Possibly salespersons. To start your next project. Don't get discouraged, that's my advice. With the right people in your team, I'm positive you can succeed.