If it were me, I’d send a follow-up letter pointing out my previous mistake, apologise profusely, and include a corrected version of the application.
I’d probably also add that I’d completely understand if the previous application had been dismissed out-of-hand due to the omitted ‘s’, but that I felt it important to let JHU know (a) I’d made a mistake, (b) sought advice, and © would very much welcome the opportunity to correct the mistake.