This is a decent mosaic, and does a good job of capturing the pixelated character. Having done this before, I hope you don't mind if I mention a few ways this could be improved.
First of all, color consistency would've been nice, but I understand that you might have a limited supply of sockets. Honestly, the wide variety of colors that these sockets come in make them great for mosaics, but you do end up needing quite a few, don't ya. Still, having all the blues in a single shade would've helped. In that same idea, I would've also used the same type of mold throughout; you have old style and new style intermixed. Again, it depends on what you have on hand, but yeah.
Now, the biggest problem with this is clearly the blue +0 pieces. The naive choice would be to use only black ones, but those are hard to find (not to mention expensive in the secondary market.) But why should you be limited to that single piece. I would suggest black 3L axels; you could still connect them to liftarms in the back and use stopper pieces to hold them in. Since you're only worried about how this looks on one side, it wouldn't be an issue to bulk up the back, and if you wanted you could even build a technic stand to hold it upright. But it would get rid of all those unwanted blue pins and replace them with reletively common elements that will get the job done.
Anyway, good luck in the contest. I'm waiting to see even more of these socket mosaics pop up here now.
I had my hands tied on colour and style; I was hoping I could get by with at least the same old-style socket even if the colours didn't quite match, but no luck (in person, the colours blend nicer, I didn't notice how they came out in the photos until after uploading them and taking another look at them). On both points, I do agree.
The axles are a great idea, I didn't even consider using them. They would've definitely worked better, I'll keep that in mind if ever I do something similar again.
Your suggestions are very appreciated!