HELP- 2001 Jetta engine misfire

hey guys I have a question for you? I just had the valve cover done on my 2.0L engine at the shop and 10 - 15 minutes after we left the engine light came on and started flashing and the engine started missing. I checked the code which is now a p0302 missfire detected in cylinder 2.

now for the question. what would cause this problem after the car was just serviced for a valve cover replacement?

thanks.

check and see if the spark plug wires are on all the way. The #2 is the second one from the belts