Sorry, I won't try and find all the tall pixel errors like I've done with the others, but I will tell you that there are a LOT of tall pixel errors. As mentioned in the forum, every pixel must be double the usual height. Have a look at the grid provided with the challenge.
Also, where's the background? The challenge calls for no transparency.
I really like your drawing, but, I agree with skamocore. Read the rules for the challenge again and fix the piece.