Hi, thanks!
If you're talking about filling the red bar while stroking, that's actually intended. Once it's filled a little, you'll be able to lift the skirt.
The mechanic also depends a lot on how fast you move the mouse, so you shouldn't need to swipe across your entire desk. You can check whether your sensitivity is high enough by looking at the circle on the left. If you can fill it without much trouble by moving the mouse quickly, then everything is working as intended.
Though to be fair, my arm was definitely sore after every playtest too... just at a later stage of the game.