delete gmail from the mail, contacts, and calendars form "settings" go to the mail contacts calander and click on mail and delete the account form there...you are already using the "gmail app" so you don't need it set up for the ipad to use as the default client.
not sure about gmail..but i would send yourself an email and then delete from the ipad app then go your computer and see if it is there when you log into your gmail account