My first impression of your picture is that you probably spent longer setting up your props than you did setting up your shot. And this was a really GREAT prop - well done for that, it must have taken a lot of effort.
Your concept for this picture fits the challenge very nicely on two counts - the pi shape and the pizza pie - so well done on meeting the challenge. The arrangement and lighting is a little conventional. I think this could have been made more dramatic by shooting at a lower angle and being bolder with your use of lights. You might also have used a shiny metal tray as a backdrop instead of that brown cloth - a reflective metal surface would have made a nice contrast to the organic looking food.
Your focus looks good and the exposure is fine. More light in the scene would have given your exposure more interest but the biggest culprit isnt the lack of light it's the dark background. Your composition is good and the border lifts the picture a little.
Overall - I think you set out with a very strong idea of what subject you wanted to shoot but you let yourself get distracted into making that before you'd really thought about how you were going to shoot it.
I tried to do this same picture -- I cut out a tortilla into the pi shape and then put the toppings on it, and it didn't work at all as a photo (though it tasted good). It looks like you did the opposite -- make the pizza and then cut it out. Very nicely, I might add -- it makes a very appetizing-looking pi on that background!
After having seen this I just have to stop voting to have lunch! It looks very delicious (extra point!). I hope you didn't eat it all yourself???? Great colors, nice crop, background and border fit and most of all it meets the challenge bang on! Congratulations.