I tried to pull the lower unit off to check my impeller and got the shift link undone and free and the lower unit would still not slide off. Then I forced it down and the lower unit came off. The only problem is that the drive shaft is still in the engine.
Did I screw up bad? Why did this happen? Was I supposed to unscrew the drive shaft somehow?
Probably not a huge issue, except that the driveshaft is stuck in the powerhead. It is a splined shaft on that end and is not screwed in. It is supposed to just slide out of the powerhead. Hopefully the water pump seals or housing were not damaged by pulling the water pump impeller key through with the driveshaft.
See if you can get some lubricant up the driveshaft to where it goes into the powerhead. I usually have had to turn the motor upside down to do this.
You can try clamping vice grips onto an area that there's no seals and tap on them with a hammer. Or as mentioned above, turn the engine upside down and run penetrating fluid down the shaft. It will eventually loosen the grip. when you reinstall it, clean off the rust and lightly grease the spline but not the end of the driveshaft...