English budgies need to moult a couple of times before all their feathers are adult size.
And not all English budgies are created equal. There is a huge difference between exhibition show budgies, and pet quality english budgies. Just like other "show" pets like dogs, just because it's purebred, doesn't mean that it is a show quality animal.
I'm sure your bird will be spectacular once it is all grown up and has all it's adult feathers. Can you post some pics? I'd love to see him