Base layers wall constricts or pulls in

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Bottom layer is smaller than the walls

I have done 3 different prints, all modeled by myself in fusion360 and then sliced in Bambu Studio. All examples are with a “bottom” and then freestanding walls on top. In all three prints the bottom is narrower than the walls and then make a dividing line. It’s anycubic pla, it’s my only choice of pla at the moment. What am I doing wrong? [IMG_5799]