First, if you click the start credits screen repeatedly the INSERT COIN text will keep flashing over and over.
Next, if you are going to make this keyboard only controls then why even have mouse controls just for the menus? Clunky, and you can't make this work with controller. Get rid of the mouse and make it keyboard only (then you can add controller support).
Finally, the keyboard controls are too crowded because you made movement WASD then made actions JKL. Make the movement arrows and the actions ZXC, and change the selection button from Enter to Space.
Nice challenge, good enemy variety, endearing graphics, and level design that makes a player want to do time trials. This could be a full game.