Crosses can be difficult to sex due to the different genes they inherit. Any idea what they were crossed with? They are very pretty.
With Pekin bantams it's usually the sprouting wattles that give the boys away, as well as a comb that gets big quickly and turns quite pink. Here's a boy and a girl at 6 weeks so you can see the difference.
But I have had a little chick that got a pink comb quickly and I was sure it was a boy due to it's behaviour (very rooish), but she turned out to be a sweet little pullet. Here's a picture of her with her rather pink comb. She is a month old in this picture.
So I wouldn't worry too much and I'd give it a couple more weeks then give us some more pictures to look at.