Nice overall for being new to pixelart. You lines are very dirty (messy) and lines are important to have clean in pixelart. The problem you have here is the CGd circles in the BG which have artifacts so maybe its your app settings. See and use the forum.

Thanks for the feedback! The canvas had to be 480x800 since the game is for Android and that's the fixed resolution, so I can't decrease the canvas size unfortunately. :(

all is right. I'm liked the style . but I think you need to draw on a smaller canvas size.
there are much places with only filled color.