I just played your game. LOVE IT!
Regarding your image distortions...
Are you, by any change, adjusting the sprite sizes by pulling the handles to make the images larger? (Just a wild guess)
I use images, even lines of text (copyright etc.) which I export to .png image format and there is no distortion.
Let's start there for now.
If yes, just make the buttons and icons the size you want them to be and don't adjust them further unless you do it by opening the sprite and make size changes there.
To find out if sizes have been manipulated, click on a image sprite or icon and then on the "Make 1:1" link (Properties panel). If the size changes, then you found your culprit.
Let us know.