Should I delete my question on Stack Exchange to reduce my own plagiarism? I created a new account and posted a question on Math Stack Exchange asking help for a specific part in an exercise from class. It was duly answered. 

That question went on to gain a lot of hits and I received an email notification which I had set, of a comment left by a person who said I was stuck too. I didn’t know him as the class strength is around a hundred, but on checking on social media, he turned out to be my classmate. Now with nearly eighty hits on it, presumably from my classmates looking at this problem, should I delete it because I feel that Turnitin would end up holding me guilty for plagiarism from my own content if other students post it before me?

I did attach my files and everything including the idea which should easily enable anybody else from my very class to use it in the assignment.

So is it wise for me to delete the question now or is it too late? Is it ethical for the community at Math Stack Exchange to lose a question that garnered so much attention and I did gain my share of points. Will I lose my points as well?
From what you have reported, it does not sound like you have committed plagiarism, i.e., you have not claimed the work of anyone else as your own work.  So you don't need to worry about that---and if other people steal your work, that is their fault and not yours.

You might, however, also be concerned that you have broken a class policy on obtaining outside help, and that you might be exposed by others plagiarizing you.  If you have not broken class policy, then don't worry about it.  If you have broken class policy, then 1) don't do it again in the future, and 2) trying to hide it probably won't help you, since this site gets widely copied and cached in any case.