That generally looks like a fine design. I can't download to double-check so just be sure:
* The background (showing as white) is 100% transparent;
* Your work is saved as a 32-bit non-interlaced PNG (that is, 24-bit color with an 8-bit alpha channel, which many graphics programs confusingly call "24-bit" all the same).
The thumbnail looks a bit messed up, which is why you should double check the format. If you don't know how to do that, let us know what graphics program you're using and someone can probably advise what you need to do
