What is causing this pattern in the first layer?

Flashforge creator pro 2 with PLA, standard quality preset, textured removable magnetic bed on the build plate.

The first lines are straight, but as it makes more parallel lines to build the layer, it starts to develop a scalloped pattern. This creates issues with smoothness when it fills back to join it from the other side later. I've leveled the build plate, although I suspect it's not perfectly flat and maybe slightly higher in the middle. Is this my problem? It appears to have the pattern even away from the middle if that makes sense.