I was playing around with it till I clicked something somewhere near my left ctrl button and it multiplied my stuff by god knows how much... (I fixed it by just copying the artwork into a new canvas, but what do I do if this happens next time? I can't seem to simply just undo it.

This is Wrap around mode(https://krita.org/item/new-wraparound-tool/), which helps creating seamless texture.
You can toggle the mode in main menu View > Wrap Around Mode, or default hotkey W key.
https://docs.krita.org/View_Menu