Disassembled and reassembled, now my display shows weird colours
I spilled some liquid on my late 2011 MBP keyboard around the arrow keys a few days ago. Immediately powered it off, flipped it upside down, left it like that to drip out for about 5 minutes before I wiped the keyboard and then removed the back cover to check for internal leaks. While at it I used a can of compressed air to clean out the last year's accumulation of dust.
Wanting to make sure there were no signs of liquid around the keyboard on the inside I followed ifixit's guide to removing the outer case up to the point where you remove the expresscard cage but got stuck with some screws that refused to turn, so I used the compressed air to blow as much liquid out of the keyboard as possible (while still upside-down) and then decided to leave the laptop open and upside-down for two days to dry out. The logic board was completely removed during this period and there wasn't a drop of liquid on it or visible anywhere inside the laptop.
I re-assembled it following the instructions carefully, and everything but the left and right arrow keys works great... except for my display. The first time I turned it on there were tiny vertical lines on the grey startup screen and all blacks were bright red, so I backed up my harddrive, did a PRAM and SMC reset with no luck, then opened it back up and removed and re-inserted the display cable. Now blacks are black again, but the display still has vertical lines on grey and generally weird colours in addition to some colours flickering. I hooked up an external display and there are no issues on that screen, just the laptop's.
My laptop was fixed by Apple previously as part of the repair program due to similar display issues (vertical grey and pink lines on startup) which I was under the impression meant it got a new logic board. Unrelated but I've also upgraded the RAM (installed 2012) and a new SSHD (installed 2016) myself.
Any ideas for what I did wrong to cause this and what I can do to fix it?