Do not fear, DVD Shrink is not keeping space, you just forgot to delete all there is to delete. Look for directories with names of the DVD-Videos, also look for directories VIDEO_TS, also look for directories DVD-VIDEO, etc.
I suggest you run Search/Find on all the drives, based on files size greater than say 10MB, so you see where you need to delete.
Also, in case you have bad allocations, use the "check error" Tools in the drives properties.
In any case, it is good idea to defrag the partition from time to time.