hi!
sorry to hear about the platforming jank! like most games, the game needs to run above a certain framerate to actually work correctly. it sounds like because of low framerates, the physics calculations for the platforming seem to be misfiring.
try this! i didn't include a way to change the display resolution in game since this was a small project, but, if you right click on the game's exe, and hit "create shortcut", and then right click on the created shortcut, go to properties, look for the "target" line under the "shortcut" tab, and add " -screen-height 480 -screen-width 848" (without the quotes) to the very end of the line, it should down the display resolution of the game and bump up your performance quite a bit! (you can shrink it even more! just make sure whatever resolution you put in instead is at a 16:9 aspect ratio!)
or if that's too confusing or too much work I totally understand! just wanted to send a solution your way! ;)
either way, thanks for playing!