The choice to mix platforming with rpg elements is pretty cool. But there are a few things that need attention. A scrolling or even static background would help the colors pop more. The coins need to get destroyed after the player interacts with them. The enemies can be killed at the edge of the screen right now and as such take away from the challenge. Maybe use a projectile or some other kind of attack that relies on either proximity or a direct line of sight?
As for the screen size, it fit mine perfectly, but the clouds need to generate outside the camera boundaries. Otherwise they're popping in and out of existence.
All the best.