Not to worry, the lone seedling seems to be up-righting itself on its own now.

Yes, the seedling will straighten itself out but it needs to come out of the heat now it has germinated. We don't know where you are located but mangetout are pretty hardy and in fact they don't need a heated propagator. I am guessing from the language that perhaps you are in the U.K.? In which case they can be sown outside in the ground. Mine are several of inches tall out on the allotment.

They are doing just fine I think, the one on the far right was the seedling in question on my original comment. Nearly 2 weeks since sprouting. I am indeed in the U.K. Many thanks for your reply.

I'd get those hardened of asap and out in the garden. Good luck.