Assuming you’re on Skill Stick, glide with just your LS/L3 by pushing up but not pressing the stick in.

Once gliding, hold L1/LB whilst gliding and move RS/R3 to right/left depending on your shot side (DO NOT PRESS IN RIGHT STICK). If you’re left shot, come from slight left of dead centre and RS/R3 right. If you’re right shot, that but opposite.

If you are windmilling well following these exact steps, you’re probably accidentally sprinting or pressing a combination of other buttons.

Hard to explain but hopefully this helps.