Hi Shannon, Welcome to the forum. I have to say a better scan would be beneficial to determining the classification of your stamp. Values of the A6a, in the Scott catalogue are for stamps with the lines on at least 3 sides of the image area. Since you have none, I'd say you're out of luck from the very beginning. I should think you should see some remnant of line on the top and left side of your stamp, but I see no indication at all. Again a better scan would help.
From what I see I think your stamp is a A7, or #11. If it were a #12 there would be very thin lines around the outside of the corners, but from what I can see of the border and portrait, I think you definately have a #11 (A7)
FYI, if it were a #10 (A6a) all four lines around the stamp would bring you 300-400% of catalogue value.
For more info on these stamps I recommend you check out
www.jlkstamps.com He's got an amazing site with lots of info.