|hmm, I'm not familiar with the program you're using, but it looks like you figured out the sizing thing.
as for the photo, I think it would have faired better if you had put the focus on the front side end of the closest battery instead of the left-side one. DPC likes a really sharp focus point, maybe try a sharpening tool.
another suggestion I might have for you would be to use a colored piece of paper as a background to give this shot more interest.
I really like the shallow depth of field and the composition that you used; this was a hard challenge to do for your first time
As a general piece of advice for a newbie, DPC seems to like very colorful, very sharp images...
Anyhow, a 4.6 is not a bad score for your first shot, this is a really tough crowd and if you take everything here with a grain of salt, you'll be a pro in no time!