m0useanswered grow question a year ago Don't apply any liquid in full sun/intense light as it burns the leaves. referrer to the directions on the neem oil container. It might have needed dilution.
I would pop another seed into a new container and bleach your grow space. That medium looks to have mites in it and that will fuck up your new seedling as well. Get a new bag of potting soil for the new seeds and clean all containers in some bleach if reusing them.
Good Luck!