Welcome to the forums @TedTomato
Other than your retention settings, yes just run the backup again. Due to your retention settings the original backup containing that extra 50GB of data will not be removed until a year passes.
To make it flush out sooner adjust your retention settings to either “Delete backups that are older than” and give it a value greater than when the last backup occurred or set it to “Keep a specific number of backups” with a value of 1. Once the backup runs a second time it will clean up that 50GBs and use that backup as the base, next return the retention setting to “Smart backup retention” and proceed from there.
This backup shouldn’t take as long as the first backup did but it will have some heavy lifting to do while it figures out where that 50GBs of data is located and how many dblock files need to be re-written. Once you get to a steady state where big deletions or file system changes are not huge (less than a few GB), subsequent backups will be much quicker.