The left edge of your 45 fill looks perfect, but the right edge is pulling inward. Cause: The 45° angle is creating an asymmetrical pull vector. Fix: Do not keep the angle at exactly 45°. Try 135° (which is the same as -45°). This mirrors the stitch direction and balances the pull. Many pros use alternating 45° and 135° split fills for massive areas.
The term "45" almost certainly refers to , the predecessor to the current e4.6 version. wilcom embroidery 45 hot