If everything on the HDD is in a single partition, you've got a problem.
You can't fit 1.2 TB into a half TB and you can't readily transfer "just the OS".
Cloning is typically "all or nothing" on the entire drive.
Imaging is a similar process that works on a partition by partition basis, but that won't help you if everything is on C.
There might be some extreme tactic that would at least allow you to try to transfer the OS only, but I can't recall hearing about any success doing it.
You could get a larger drive?
Or you could do a clean install to the SSD and keep all your data on the larger HDD.
Or maybe move some personal data off the HDD to an external so that C is a lot smaller...I have no idea what you have on the HDD.
Maybe you can't whittle down the 1.2 TB at all?