Okay so I can tell you're trying to mimic the style of the show and tha alone you seem to be doing alright with, although your lines are a little shaky but that's understandable since most beginning artists are.
I think your biggest issue is definitely with your coloring. I don't know what program you draw with but there are a number of ways you can fix it. One would be the fill tool, although I don't always recommend it since it can leave a wired white space between your lines and color.
The second option that I recommend is selecting the space inside it. You can do this by selecting a square around it and then using the magic wand to delete the area around it. That probably sounds confusing but you can look up a tutorial is you need to ^^
The last option would be to use a sold brush instead of the air brush and take the time to color inside the lines on a new layer. The advantage of digital art is that you can make a new layer and put it BEHIND the lines you made so doing this is really easy, you just have to put in the effort to do it ^^
Hope this helped!