There's nothing wrong with trying your best to improve. Tweaking and fixing is great, but spending too much time making your comic better will take time away from actually giving it to the world to enjoy. Another good way to improve is to finish your stuff and put it behind you.
When I first started making comics four months ago, I never thought that I could improve, that I was at the top of my game and, arrogantly, I thought that I had the best idea for a comic EVAR! However as I've been making it, I've realized that there was room for improvement, despite what I thought before.(Actually, there was a ton of room for improvement) And now, looking back, I know how much I've improved on, and it's a great refreshment to look at comparisons of my current art to my older art.
In other words, just keep making comics and stop worrying about fixing mistakes. As you go along and acknowledge them, you're less likely to make another, and your comic will get better and better.