Store category buttons should be square all across the board. In this store https://www.zazzle.com/store/abbyjuliart the first category Accessories is the perfect size. The rest look unprofessional because they are not all the same size.
My suggestion is to go to the bottom of Zazzle's page and to to Help > Selling and start there by reading their help articles. There are so many aspects that go into a successful store and they are not all to do with how your store looks.
There are also free help videos HERE on YouTube.
