No matter how hard you try, how much effort you put into a work or how much time you devote to your art, it will never be perfect. Nobody creates perfect art; every artist that has or will ever take up their tools will eventually find something wrong with everything they do. It’s the nature of the beast. An artist can always find a flaw in their own works; there’s always that line out of place or that color that’s slightly the wrong hue.
However, there’s one little thing about this that you need to keep in mind. Other people won’t care. Many won’t even notice the mistakes. You might be able to see every flaw, but odds are that other people will simply see a pretty image.
One example here is that straight lines can actually suck the life out of an image. Imperfect lines can actually liven up images.
In the picture above, the pencil on the left is made of entirely straight lines. It’s “flawless”, so to speak, because every line is perfectly straight: there’s no curves anywhere. The pencil on the right was made by loosely tracing the one on the left, with the lines curving or bending anyway they wanted. Which of the two looks more “alive” or “real” to you?
In fact, while there are plenty of tutorials on this site, these are there to help guide you, but not to restrain you. They are provided so that you can find an easy way to produce the same image twice or more. However, you don’t have to do things the way I’ve described. Indeed, finding your own way to do things can actually improve your own skills.
In the end, always keep trying, and always keep looking for ways to improve. There will always be something you can improve on.