You can check your meta tags by viewing the source of any page in your cafepress shop.
When you look at the Meta Keywords and Meta Description, you can check to see if it matches what you input for your shop info.
I think some meta information is generated automatically (like on the product level) and some comes from what you put in (like on the main shop homepage)
I wouldn't worry too much about the fluccuations in google. There are about 5 dozen things that could have caused it, many of those things you have no control over.
Most of what you read will "speculation" on what people guess is happening, but if you start messing around with stuff, you could break something that doesn't need fixing.
Sometimes in a month or so, your rankings come right back to where they were.