According to MAH CET 2018 brochure, you are allowed to modify details only before you hit on the "Final Submit" button.

Since the error is only in mother's name, I think it should not be an issue.

What needs to be with out errors is:
" The Name of the candidate or his /her Father/ Husband etc. should be spelt correctly in the application as it appears in the Certificates/ Mark sheets/Identity proof". Also the name on your Admit card/Hall ticket should match exactly with the ID proof you are carrying.