Well I figured it out on my own. I did have to unmount the system and remount it. However, in between I had to resize the actual filesystem to match the partition size. Here's how for anyone else who is curious:
1. You have to boot from a rescue disc or a liveCD distro like knoppix
# resize2fs /dev/hda1
There are also options you can change if you don't want the filesystem to fill the whole partition. Read the manpages. Now mind you, this is AFTER I had already used fdisk to change the partition size. You can do the fdisk step after you resize the file system, but you should also do that while in the rescue or liveCD.