You can push it in with a little force as there is a cavity underneath the trem system.
A quick fix is to wrap a bit of tape around the bottom of the arm. But if you look at the diagrams on this page;
http://www.webrocker.de/jaguar/cms/2007/05/12/setup-the-tremolo-system/
You should get a better idea of what is going on under the trem. You may be able to tighten the collet, i forget now as it is some time since i messed with the trem.
What model Jaguar do you have? Generally AVRI tremelos are viewed as the best, then CIJ then the dreaded allparts replacement.