If I understood your question correctly, what you can do is to create another one on your phone (with the correct details)
Go to the settings menu --> Accounts & sync --> Add account --> Google ( Enter the details)
Once you have done so you will see the new account in the Accounts & sync menu.
To delete the wrong e-mail address, press and hold down on the wrong e-mail address and a pop up menu will appear with an option to delete it.
Now if the new account details are the same as those you used before when you set up the phone, in theory you should be able to access the A.M. now.
Note: The reason why you could not delete the e-mail account on your phone as it was the only one associated with the phone.
Once you have two or more, then you can choose which one you want to delete.
