The CD version and the online version are two physically separate products that do not talk or integrate with each other. So what are you wanting to use for your 2018 taxes? The CD version or the online version? Regardless of which you choose, we can help you with importing from the .tax2017 file once we know:

1) What you want to use for 2018, and
2) What you used to complete and file your 2017 return.

The Online version is not as fully-featured as the desktop version.   Some of the Online editions have form limitations that the desktop version does not have.

 What edition of TurboTax did you buy?  It may include a state program (if you need one), while in the Online version a state return has an extra 39.99 preparation fee.

Desktop TurboTax has the popular Forms Mode for direct viewing/editing/printing of forms during preparation.  Online TurboTax does not have that feature.   

Desktop TurboTax can prepare multiple Federal returns, while Online TurboTax can only prepare 1 Federal return per account.

If you are sure you want to use the Online product, we can tell you how to get a refund for your desktop software purchase.  If you want to stick with the desktop product you purchased, as Carl mentioned above we can tell you how to transfer your *.tax2017 data file into it.

If you want to transfer a 2017 return into the Desktop program.  Transfer from Online into the Windows Desktop program.   Expand the 3rd blue link
<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/1901506-transfer-last-year-s-return-into-turbotax-for-windows">htt...>

One way is to start a 2018 Online return and transfer into that.  Then you can download the .tax2018 file from online and just OPEN it in the Desktop program.

I bought the premier version. I don't need the state tax piece even though it comes with it since my state doesn't have state taxes. Once my 2018 return is complete, will I be able to load the file to my online account? I'm OK using the desktop version, I just want all my files in one place. I already exported my 2017 data file and loaded to the desktop version.

"Once my 2018 return is complete, will I be able to load the file to my online account?"
No. But so long as it's on your computer next year for the 2019 tax return, you will be able to import your data from the .tax2018 file on your computer, into the online version of TurboTax 2019.
If you use the desktop version of TurboTax 2018 to prepare and file your 2018 tax return, then your computer is the only place that original 2018 tax file will exist. So you'll want to make backups when done of course, in case something happens with your computer over the next year and you lose it.
Your other option, which means you'll pay for both the CD and the TurboTax online program, is to complete your 2018 return with desktop, and then e-file it using the online version *after* you pay your online program and filing fees. That would be rather costly I think, and not worth it.