You can - and should - add the actual recording of your song. There are many reasons to do this, and one of them is to be able to take advantage of Sentric's sync opportunities.
Manually Adding a New Recording To a Song
Once you have added a song to your account, go to it, by selecting 'Songs' from the menu. Scroll down to the Song Library.
Select the song you want to add a recording to, then click on the '+ Add new recording' link, on the right-hand side of it.
You can search for your recording on Spotify, if you have this linked to your account.
If you are adding it manually, fill out all of the fields, as best as you can. If you are able to upload a .mp3 file of your recording this will help you be considered for exclusive sync opportunities for film, tv, etc.
Once you have added all the recording data, click on 'add recording' button at the bottom of the screen.
Adding a New Recording From Spotify
After having added a song to your account, go to it, by selecting 'Songs' from the menu. Under the Spotify song suggestions section, search for the song from Spotify, by its name. This will search your linked Spotify account for that song.
Once you find the song from the listed results, click on it. Make sure that this is the correct song, based on its information. Select the option 'Yes, add this to my song list'. Then select the option 'This is an alternate version of a song I've already added'.
Then, select the exact song this new recording should be added to from the dropdown list - by clicking on the song name underneath. Click on the 'add recording' button.