Sorry you can't finish online.  You have to download the .tax2015 file and open it in the 2015 Desktop program installed on your computer.  If you paid for the Online version you can call in and ask for the Desktop program to finish.

Here's how to finish
https://ttlc.intuit.com/replies/4186197

Contact Customer Service 

https://ttlc.intuit.com/replies/3300041