Looks like a normal young plant to me!
If it's comforting to know, one of mine was a helmet-head and for the first couple of weeks, grew very slowly with "mutant" leaves. It's now flourishing! You wouldn't even know of its wayward beginnings haha!
The only thing I'd suggest is to try and get your temp up, as 15c is a little on the cool side! Good luck w your grow!!