You can also partition it by reinstalling from scratch and setting the partition sizes to be what you want them to be from the get-go. Of course, that will involve wiping everything on the system, but you'll get your partition sizes.

I still believe that it is appropriate to partition for servers but it is not particularly compelling these days on a laptop/desktop, IMO. There is no performance benefit and it is all on the same hardware so no real protection against the drive dying and still getting your data back.

I'd probably just stick with the 300GB+ drive and not worry about it.