Welcome to the community, Trent!
Can you please provide more details about your whole system configuration? Is this your booting/primary HDD or is it a secondary one?
In order to be able to use its full 3 TB capacity, you'd need
to re-initialize the HDD in GPT (GUID Partition Table) instead of MBR (Master Boot Record). MBR works with disks up to 2 TB in size and it cannot handle more than that, even if you try to extend partitions.
I'd suggest you backup any files you might have stored on the 2 TB partition and re-format the drive using the other partition table (GPT). It's associated with UEFI and replaces MBR because it doesn't have the same capacity limitations.
If this is your booting HDD, you'd need a UEFI -based...