Good work. I didn't spot any glaring inaccuracies. I think the SMB side should be more orange, but that's just my OCD talking..
So what do the top and bottom sides look like? Have you/are you going to decorate them? My suggestion for the underside would be a dark blue colored ?-block (as seen in SMB, New SMB, and New SMBW), and the top side be either a dice block (to represent the Mario Party series) or just leave it alone (so you can tell which way is up on the awesome box).