why is the shape key shrinking mesh when all i’m doing is rotating 90 degrees on z axis?

Hey Clayton, for which part are you needing to use a shape key at this point in the process? 

Shape keys just store the location data for each vertex, so by rotating the mesh it edit mode it’s just following a straight line from one position to the next for individual vertices. This could definitely cause it to look like it shrinks before getting to the final position. For rotations, it’s probably best to animate it in object mode.