Hi! This is pretty good for a first project! One major suggestion though!
Right now, your controls are really spread out, and it makes it annoying to start over. Having to move my right hand to the mouse to click restart, then to enter to play again, even though its like 5 seconds, feels really tedious to try again.
It'd be better if those were relegated to just one button, or have an extra option.
My suggestion would be to have "retry" be selected by default, and have space be the button to choose an option.
Maybe the beginning of each level can have a little buffer for the player to run on, and make space the button to start the game so we can just press space to get right back to the game when we die.
Also, I noticed that you can jump while not on the ground, not sure if intended.
Good job for your first project!