Having trouble mounting dust cover on Z1r caliper

I have spent way too much time fighting with this dust cover. I am hoping there is some simple technique that I haven't figured out. I actaully had it on and then accidentally pulled it back off unmasking after paint. I have been using a small allen wrench to work it in the grove around the back but just could get it to work tonight. Thanks.

patience is all i can say,unless its stretched out of shape then its time for a new one