Weaver mount red dot on Picatinny base?

[RG43]

I've got a Sight Mark Ultra Shot reflex sight with a Weaver mount I want to put on my Buckmark Field Target 22 pistol that has a Picatinny base on the top. The sight will mount on there, but it's rather loose, so I'm sure the accuracy would be poor at best. Is there a way to make it fit snuggly? Or am I crap out of luck and should have bought a different sight?

 

[RG43]

Nevermind, I figured it out. I just needed to tighten the screw on the other end of the quick release lever. That tightened up the mount and now it doesn't move around.