R-Drive Image ALWAYS keep one backup set - which is one full backup and several incremental/differential ones, even if it exceeds specified parameters, like the number of files. You created a script for one type of a backup - a differential one. You need to create another one - for a full backup, and run it regularly.
Working with backup sets is explained in our online help: Backup Sets
. Please note that 2 tasks/scripts are used in its example, one that creates a full backup and another to create differential images.