You'll need to make and "adjustment" or ReFile your 2018 return as any contributions made in the First 60 Days of 2019 must be included on the 2018 return.
The ReFile service for TurboTax Online users is not available until April, but you can do an adjustment online if you have a CRA My Account set up.
CRA requires that you wait until you receive your Notice Of Assessment before you make any adjustments or ReFile that tax return. Here's instructions on how to go about that: https://turbotax.community.intuit.ca/replies/2647992