Well, I am not familiar with the sebright. I looked for a good thread to check out, but it seems that they are older. You can check them out though, maybe someone will see that it's been posted on...just type in Sebright thread in the search bar..take your pick on which thread, or, just check them all out.
Pretty bird you have.
Wait, found one from this yr..just weeks ago posted.
I'd say it's a pullet with so little comb development and no hint of pink in it. Most bantams you know for sure which way they are going by 6 weeks so you should know soon. Watch out for wattle development. Pullets won't start growing wattles until around 12 weeks but boys come in fast and bright pink/red. Just so you know, Sebright hens are known to crow so don't assume you have a boy because it crows.