Ian, I am playing the tiny violin in mourning for this plant. If it looks like that (even bigger) after 5 weeks, probably just about everything is wrong. The most likely advice you'll get from the experts here is a request more for imformation about your grow, but also to go the GROW GUIDES, read everything there.
Identify what you did differently than what is in the grow guide, throw that baby out with the dirty bathwater
, get some new seeds and start over.
Ok, you don't have to toss it, but I think it would be a more positive experience to start anew at the same time!