[BananaMilk]

When I try to restab, my legs bend up, Should I duct tape my legs?

[BboyMyth]

too much trouble... just practice keeping your legs straight by being conscious of it every time you windmill.

plus, it'll help you develop better training habits

[NiSenNen]

Yeah, your mills aren't THAT bad.
Stretching helps your body keep form in mind.
Try some split stretches in between mills.
You have to will yourself to keep your legs straight.