As far as I know, Mylan doesn't make a gel patch. You probably have plastic matrix patches, in which case the best way to use it is to simply wear it as intended. Pick a spot to place the patch, wash and dry the area well.
The less hair on the area the better. Once you've put the patch on, leave it on. Removing it and re-applying it will leave you with a bunch of dead skin stuck to the adhesive which really gums up the works and makes it a pain in the ass to re-apply.
Fentanyl is a seriously potent drug, and you need to watch your step even if you have an opiate tolerance. It will take awhile for it to build up and start to take effect. Be patient. Several hours may pass but it will work as promised sooner or later. Heat may be applied in intervals to speed the release of the drug, but don't go crazy with it.
There is excellent information here at Bluelight on these patches, how to use them, etc. A simple search will probably yield more information than you could ever want on the subject.
If you start to feel sick, or you go pale, remove the patch as soon as possible. You shouldn't sleep with it on at first, either. Fentanyl has claimed too many Bluelighters, it's important to be cautious.
EDIT: Just read that you had already eaten it....