I needed to enter the identidy theft pin from the IRS, however I e-filed without entering it. Is their a way to go back and enter the IP-Pin?

No. You will have to wait and see if the IRS rejects your e-filed return. If they reject it, then you can enter the IP PIN then. If they accept it, then you're done filing your return for the year and will just have to wait it out.

If you have an Identity Protection PIN and you did not enter it, your return will probably be rejected.  When it is, enter your PIN and re-file the return. 

To enter an Identify Protection PIN for you, your spouse, or dependent please follow these steps:

1. Click on Federal  > Other Tax Situations
2. In the Other Return Info section, click on the Start/Revisit box next to Identity Protection PIN.  [See Screenshot #1, below.]
3. On the next screen, mark the button  Yes, at least one of us got an IP PIN and click Continue. [Screenshot #2]
4. On the next screen, Tell us your IP PIN, enter the IP PIN for you, your spouse, or dependent.  Enter an IP PIN only for the people who have them. [Screenshot #3]
5. Click Continue and proceed with re-filing the return.