So long as the bubbles on the level are inside the lines all should be okay, what happens if not level is the ammonia will pool and you loose the natural flow of fluid and loss of cooling .
You should have a fridge manual which will detail the fitting instructions of the unit, many times the units aren't fitted correctly, som a read of that and a squiz behind the vents will confirm if its been fitted correctly but even with the rear all correctly fitted, fans installed they will drop in performance over 30 deg.
As Boots mentioned there are a number of detailed threads describing how to mod the fridge with rear fans and stuff.
When I get home from this run I will be pulling my unit out and seeing what else I can do to insulate the outer wall and make a better flue, all to improve the air flow and dissipate the heat, have to keep it balanced though as they operate around the 50 deg mark.