All the images and animations are rendered out at 720p to save on filesize (anything above 2GB means Android users can't install it) so if you're stretching or fullscreen-ing your game that'll make it seem fuzzy.
As for no graphics settings, it's a 2D rendered game. You can't adjust graphics because everything is baked in to each image, unlike a 3D game where a lot of the graphical processing is done dynamically.