Monitor Mount to Desk With Slanted Bottom

[Vpython]

I have a dual monitor mount and I am wondering how to better secure it to the bottom of the desk that is it is currently attatched to. The bottom of the desk is not flat at first, it is slated down towards the floor slightly and then levels off. The clamp only reachwa the middle of the slant so it is unable to clamp to the flat part. I have cardboard shoved in place to account for the slant, but I would rather have a better solution since the clamp is slowly slipping.
Thanks.

 

[giantbucket]

find someone with a table saw and ask them to make you some wedges. or hit up your local lumber yard and see if they stock shims (wood ones used to level windows during installation) that you can trim with a basic hacksaw.