HI,
Since you elected to clone your drive, MR made a clone (exact duplicate) which should be approximately the size of the original disk, leaving any additional space as unallocated. With Win 10 disk management there is an extend option but that only works if the available partition is adjacent to the partition you wish to extend. It cannot extend if there is a partition in between.
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What I do in cases like this is use MiniTool Partition Magic (Free) . Once installed and opened (viewing the disk layout at the bottom of the window), if you right click on the “C” partition you wish to extend, a drop down will pop up and you can select extend and use the choices to select the UNALLOCATED partition and select to use ALL of the unallocated space, it should move all the unallocated drive space into your C drive.
Here is my test disk example screen shot: Hope this helps
Here is the link to the software, select the Home User (Free) edition.
https://www.partitionwizard.com/
