Only the original resolutions IE 640x480 and 800x600 work when I click fullscreen, and I have 1024x600 and if I change the res manually I can only do it in windowed mode.

Full screen is done by taking a resolution and blowing it up to twice the size, that way you still get the pixelized sprites, but still full screen.

But when I press alt+enter it just gives the res whatever it may be that will work, IE 640x480 or 800x600 and all of the excess is pitch p
black so there is just a part of my screen displaying the game and then surrounding that picture like a picture frame is a black frame.

I can get a 1440:900 full screen over here, so that's complete bull♥♥♥♥. Full screen just makes it fullscreen, without the edge, stretched to whatever.
2X makes it blow up to twice the original size, with a border.