Your SLW could possibly be a rooster because of the extra white on it, but hatchery quality isn't the greatest. And Wyandottes mature early even the pullets. Dont give up on it just yet, wait a few more weeks. Here is a pic of mine when she was the same age as yours, I was sure she would be a roo.
This pic shows my 3 when they were young all pretty patchy
and here is another of my Wyandottes grown up, but shows her patchy white like yours. Her color eventually evened out as she matured though(I know she has the wrong comb type)