Texture issues

When I created my textures for my 2D game. They are coloured balls. However they look fine in photoshop and all the platforms EXCEPT Android. I have been reading online hearing a lot of strange tips such as creating separate project for Android. This doesn't seem very good for cross platform developing because that means I need to create different modified textures for each platform. Also heard a lot about ETC texture duplicates? However I do not understand it properly

Can someone explain to me what I should do in layman's terms please?

Also I noticed I have 512 x 512 textures however when I shrink the sprite the texture distorts but is perfectly fine if I stretch it out bigger than its original size. I do not understand. Any help would be much appreciated thank you!