I would suggest adding a 'shop title' (found under Your Shop: Info & Appearance) and list what you sell using key words. Ex: Oil Paintings, Watercolors, Acrylic, Originals. This will show up under your Shop Name at the top of your page, and it's one of the main places that google uses to find key words.
The other place google uses is your shop announcement. Do basically the same thing there: in the first paragraph list out what you sell and be really heavy on the key words.
I hope that helps a bit. Give google some time to update (sometimes a couple of weeks) after you make those changes.
I wish you lots of views and sales!