I will take a guess and say rooster! It's harder to tell at 3.5 weeks but we had a chick who had larger thicker legs at that age than the rest and it turned out to be a rooster. In a couple weeks (?) the comb/wattle may turn red and saddle feathers may start to show so it will be easier to tell.
There's a lot of great peeps here! Feel free to ask lots of questions. But most of all, make yourself at home. I'm so glad you decided to join the BYC family. I look forward to seeing you around the run. I think it's still to young to tell. Good luck with him/ her though.