Ideally, the rim tape should completely cover the rim from flange to flange. Unfortunately, Velox, for example, doesn't come in enough different widths for every rim. 17mm works for most road rims, but I assume your Performance rim tape is about the same and it's obviously too narrow.

One possible solution is to use that nylon reinforced strapping tape. It's easy to rip down to the exact width that you need. If you ever need to get it off, however, you're facing a royal PITA.