It is very cute, but I think it's too early to tell yet. It's comb is large for it's age though, which does lead me to suspect that you have a cockerel. It's one of those 'wait and see' situations, unfortunately... Hopefully someone who has more experience with Serama's will chime in soon
that is definitely a serama, but you might need to wait till it is older till you can recognise if it is a hen or cock.
personally i think it is a cock because the comb seems a little too big to be a hen at its age. but then i haven't had seramas before so i'm not experienced