I filed 2017 today not 2018...I already have filed my 2018.

If you efiled it after you efiled 2018, it will be rejected.
Di you still need to file a 2017 return?

Unless you PRINTED and MAILED your 2017 tax return you STILL have not filed it.  (IRS rule: You CANNOT e-file a return for any year earlier that 2018.)

and you cannot use TT online to prepare a 2017 return now./

Where can I go to file 2017

You can purchase the Desktop version (each year that you need to file) of TTax for previous years at the link below and install it on your own computer.

Previous years' TTax

http://turbotax.intuit.com/personal-taxes/past-years-products.jsp

Beware of purchasing TTax software on eBay and other secondary sources.  Not only may the software be of questionable authenticity, it may not be able to be updated so that it is usable

When mailing a printed return it is always a good idea to go to the Post Office and mail it 'Certified' with 'Return Receipt'.  That way you will have proof that they received it and when it was received.

You need a computer to use TT for 2017, not a phone.

You can only buy the download for prior years.  You need a full Windows or Mac computer to install it on.  Buy the download here     https://turbotax.intuit.com/personal-taxes/past-years-products/  

You have to print and mail prior year returns.  When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.  Don’t forget state.

If you are getting a refund, there is not a penalty for filing past the deadline.  You have 3 years to file for a refund.  If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.

How to file a prior year
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return

Or If you have a simple return You can fill out the blank forms for free.
Here are some blank forms & instructions for 2017
1040 https://www.irs.gov/pub/irs-prior/f1040--2017.pdf     
Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2017.pdf

1040A https://www.irs.gov/pub/irs-prior/f1040a--2017.pdf    
Instructions https://www.irs.gov/pub/irs-prior/i1040a--2017.pdf

1040EZ https://www.irs.gov/pub/irs-prior/f1040ez--2017.pdf    
Instructions https://www.irs.gov/pub/irs-prior/i1040ez--2017.pdf

2017 Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2017.pdf
Publication 17 Tax Guide for 2017 https://www.irs.gov/pub/irs-prior/p17--2017.pdf