Help - Part isn't printing square

I am having trouble getting my print to stay square. I am printing a 90 degree right triangle which is basically a carpenters framing square. When I print an actual box, all of the corners come out 90 degrees but when I print this right triangle that has a taller lip on one side, the corner doesn't stay 90 degrees. I think it has to do with the fact that the long side is cooling and / or shrinking faster than the short sides of the triangle because the taller lip is still printing while the long leg is able to start cooling. I think this is what is causing the print to go out of square but I am looking for some help from people who have hopefully had and overcome this issue.

Thanks for the help.

what printer, slicer setting, print and bed temperatures and speeds and what material (filamet type) you are using :-)
Oh yeah and what surface you are printing on :-)

I'm printing on a Fusion3 F400 and an Anet A8. Both are printing on a glass heated bed. Hotend at 200 degrees and the heated bed at 60 degrees using PLA. I'm using Simplify3d.

We would be willing to help.

Can you show us a picture of printed item still on bed.
Attach the Model so we can examine it. And provide us with the slicer settings used to slice the model.
It could help to know the speed at which the model was printed.