My Penimaster VAC is falling off

I have been hanging with my Penimaster Vac hanger. I started one and a half month ago with 2lbs. As I increased the weight to 4 lbs its really hard to keep it on. Vacuum cup slides off after few minutes due to weight and it drives me crazy. Does anyone have similar problems and how did you guys fixed it? Btw I am uncircumcised so I don’t know if this has to do something with that.
Sorry for broken English, I am from Sweden.

Any help would be appreciated!