As others said, increase the window size! There's no reason for it to be that small. The rules say you absolutely can do it: "You may scale the game's resolution up as long as the base resolution is still 84 x 48."
When you lose, I don't think it's necessary to go back to the main menu. It just makes restarting a bit more tedious.
I can see the appeal in the gameplay (although it is just copied from Super Hexagon), but in my opinion the player moves so fast that sometimes you overshoot and die anyway. The speed of the hexagons doesn't help, I felt sometimes like I just had to be lucky to get even the first one.