How can I get better at completing tickets?

I empathize with this a lot having also worked at an early stage startup, and you are 100% correct in that you need to put in the reps with coding. The crucial thing to do now at this stage in your career is to build an extremely solid coding foundation, which you can't do if you're unable to focus. Here's what I recommend:

• Use the app yourself outside of work where you can and don't do any other manual QA on top of that. In the meantime, push to hire a manual QA contractor and make sure that process is chugging along smoothly.
• Delegate the release management to someone else if possible as well.
• When it comes to coding, try to focus on a more specific area. Your goal is to build a "superpower" in a broadly applicable, but targeted area. A good example is "I want to get extremely good at building mobile app UIs." This space has focus, but it's still wide enough that you would own a large portion of the company's product.

All that being said, it will be hard to do this in a very small startup like yours. Do what you can, and regardless of what happens, keep an eye out for gaps that can seriously damage the company. Even though your goal is to drill down into a specific code area, that doesn't mean you should step outside of that zone when times really call for it, especially in a startup.

Related resources:

• This Is How Software Engineers Should Initially Learn
• Quickly Building Reputation As An Earlier-In-Career SWE