Sally-
 
Your paintings are sweet! Listen to the pros, get more cards up there, with different designs. . . I'm one to talk, I've been with GCU since March and only have less than 25 different cards up right now, but I have had regular sales and repeats on certain cards.  I KNOW I'd do much better with more cards.  I, too, am finding my "niche."
I think that adding cards "regularly" is a good thing, too, if you can (a "do as I say not as I do" thing here) but I find when I add new stuff I seem to get a sale. . . maybe not even what I just added.
 
About your watercolor scan issue:  I've tried putting a folded towel on top of the art and then something heavy like a large book on top.  I do this when scanning collage art (that will fit in the scanner), too.  But for larger pieces, I find photographing them works far better
 
I think you'll find a lot of good support here at GCU.  It's always going to be competitive, but the staff and the artists all help eachother out here.
 
-Ernestine