Don't trust the cat

ok...so when i started up the game it said run in 1000-something resolution or normal, and i went i guess its meant for 1000-something, so i played the game for a bit and when i quit i found that it had changed my computers resolution, i changed it back and started up tf2, i play the game on 1700 by 1200 or something, and the game was no longer streched across the screen, i tried playing a different game and i had the same results, i restarrted my computer hoping it would fix itself, but it didnt work, can someone please help?

I am thoroughly engrossed. This is masterclass in abstract indie.