I just checked my Fiskers rotary and the replacement bar is 15". I always turn mine over before replacing it. Did you try that.
I buy my replacement bars at Michaels - very inexpensive with the Fiskers trimmer stuff. In fact I bought several a few months ago but ai just bought more.
Are you sure yours has sticky tape on the back side? Mine is a bit of a struggle to pry out of the slot but there is no sticky tape.
WHen it needs to be changed I just turn it around but still on the same side so I make a new cutting groove.
Then I turn it completely over and I can make one cutting groove and then another when I turn that side around. THey seem to last 2-3 years before I have to turn them around. THe life of one of the bars for me seems to be 7-8 years using both sides and making 3 grooves in addition to the one it comes with.