I did it in paint, tracing over a pre-made pony. I just edited the ears and hair...and did a sloppy job on everything else.
The wings are a wee bit off center: they should mostly cover the cutie mark. Honestly, I think you did a really good job with this! When it comes to pictures, if the dimensions are correct and to scale, it's good! Perhaps if you had a better program to make it with, such as SAI... EDIT: That used to be my TF2 spray, Blackjack :derpe:
Also if you use Paint, there is a tool with which you can make lines and than drag them around to get them durved. I dont know the name of the tool but it is good to get this straight but rounded lines.
SAI does crazy things to ponies! Actually, Photoshop CS5 has a great inkline tool where you wouldn't even have to hand-draw anything. *Snickers.* Well, not when tracing in involved...