The bunny ear effect can be eliminated with a bit of pre planning before cutting especially if the pillow is made of plain all over fabric or has borders that are plain strips.
I have made two small example pillows from sheeting that are only 10 inches square when finished.The first one I did not modify in any way and you can see that there is a small bunny ear effect
To make one the same size without bunny ears you need to trace out the finished size of your pillow as shown with at least 1/4 inch extra all the way around
Repeat for all four sides.
You can then trim back to these lines leaving 1/4 inch for seam allowances.