How do I make it full screen? I can only play it in a small box.(I forgot how to make it big)

Hit alt-enter.

Thank you kind sir. (LOL Oblivion Reference)

Also, if you go into the config file, you can change the shader setting (looks like shader=2xwhatevershaderisdefault) and change it to shader=3xsai and it will make the gameplay window bigger.