Trouble resizing virtual box VHD disk

Did you extend the volume in the guest OS? Windows won't use the space until you tell it to do so. Microsoft has a guide on how to do this: https://docs.microsoft.com/en-us/windows-server/storage/disk-management/extend-a-basic-volume

Depending on how the disk was partitioned, you may not be able to extend it from Windows. For example, if you're trying to extend C: but there are other likely hidden partitions after it. If that is the case, you'll need to use something like GParted: https://gparted.org/ to extend C: and push the other partitions to the end of the drive.

VHD files can be configured to only take up as much space as the guest is using, I'm guessing that's why the size on disk doesn't match the capacity.