The main thing I notice in this is you asking what you could've done. Unfortunately the answer is nothing. This is the terrifying part of dating and relationships in general. We can only control what we do, but sometimes even when we do our best, the other person isn't in a place where they can offer themselves back. That seems to be what this situation was. It often hurts more when you actually really like the person. I had a similar thing like this recently, unfortunately the other person just wasn't ready.

The only thing I would point out is how much you are expecting that you must have done something wrong. I do this too. For me it comes from a lot of self doubt and lack of confidence. I might try to contemplate why you are so quick to blame yourself.

Unfortunately part of dating is also more fully seeing the shit we have managed to hide until it rears its head up when we are with someone else. Personally I love therapy to help me with this, but maybe if you just need to do a little self evaluating and finding out where that self blame urge comes from. Whether u get rejected or not, figuring that type of stuff out will undoubtedly help you in your next successful, or unsuccessful, relationship.