The slide itself is a square box that pretty much stays in square. However, depending on how you have it leveled, the frame of your camper can be flexed, which in turn can take the hole the slide fits in. As pointed out, as long as it seals, you are ok. However, I'd still be looking into why the wall is out of square.
2014 Coachmen Catalina 253RKS
2016 Keystone Summerland Mini 1750RD
2012 F250 Lariat 6.2L Crew Cab FX4
Reese dual cam SC/WDH