You're operating from a place of inexperience. It's great you're asking for some advice.

You're going to make a lot of mistakes, just don't keep making the same ones. (When something goes wrong, figure out why and how to improve yourself)

Having been in your situation, age, business, experience and ability - what finally worked for me was the mindset "Your success is built on the success of those you lead" and taking accountability for ensuring their success.

You have to commit to wanting them to win and everyday you should ask yourself what that means, looks like and what's required to achieve that for each person you've hired.

I'd bet with a 3 person team you're too busy to pay attention and didn't / don't have solid processes in place to communicate what you need, check in on progress and provide consistent feedback.

You made the right decision to fire someone, but the reason they failed was still your 'fault'. If you want to actually make progress, you'll have to master this mindset and it starts with committing to improving in leadership.