Minecraft Fullscreen Zoomed into top left corner

When I downloaded optifine for my minecraft to make my fps go up from 12 fps to 200+ fps, I pressed F11 to make it go into fullscreen to make the fps go higher. But then, it turned into fullscreen except it was zoomed into the top left corner. It worked perfectly before though. My PC resolution is 3840 x 2160. But my minecraft optifine resolution is 1280 x 720. When it is not at fullscreen the fps is like 12. That is the only way it worked before. Please help I do not know what to do.
As you notice in the pictures one is 20 fps (not in fullscreen) and the other 60 fps (full screen zoomed into one corner).