No, your design does not have to cover the whole tape. Your lines or individual elements should be at least 1mm thick. For inspiration, take a look at the FBS Mystery Pack designs from the last few years. Instead of covering the whole tape with a design or pattern, smaller patterns in the right places (rember your finger positioning) are pretty cool. Don't worry too much about the grip or performance of your design. The main thing is that you like it and would like to use it yourself.