At the end of your "always" try to reset "Touching Platform?" to 0. This way it will only be 1, if you just hit a tile, not forever after.
Besides that, enabling/disabling gravity seems like a strange (but creative
) way to make a jump.
It's probably easier to use "push Self sharply towards (xdir: 0 ydir: -1) at _ force" instead when Up was pressed.
And just a note: Instead of using a number attribute that you set to 0/1 for "Touching Platform?" you can use a boolean and set it to true/false.