So I was making an 8x8x3. I checked it and toothpicked it. Still wet. Put it back in and set another 10 minutes. I just checked it and the middle sunk!?! Why!?! Anyway to fix it. It's still not quite done in the middle so I turned the oven down a bit and I'm waiting for it to finish.

Were you at the maximum baking time when you opened the oven door to check it? Sometimes opening the oven door too soon can cause the cake to fall in the middle.....sorry once that happens, it's not gonna rise again.