After I assembled Toshiba Satellite A75 laptop back the screen is very low resolution and has wrong colors

I took apart a Toshiba Satellite A75 to clean the fans and cooling module. It was shutting down. When I put it back together the screen was very low resolution and wrong colors. Everything else seems to be working. When I plug in an external monitor it looks fine.
Did I damage the screen in some way? I thought I was being careful. Is there something that needs to be reset?

I do not think that you damaged the screen. I think the problem might be related to the video cable. Check if the video cable is seated properly on the system board. To get access to the video cable, you only have to remove the keyboard securing strip. Look inside the video connector on the system board and check if the pins are fine and not bent. Make sure that the video cable connector is seated properly.
If you took apart the display assembly too, then check the connection on the back of the LCD screen.