Should I delete my question on Stack Exchange to reduce my own plagiarism?
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.