|When you try to resize the filesystem, are you entering numbers in the edit boxes, or using the slider? gparted won't resize the filesystem if the "Free Space Following" box is 0. Using the slider, the Free space following will automatically be filled in as you move the right-hand endpoint.
A quick google search doesn't suggest that there are any issues with resize2fs, and in any case, if you watch the gparted screen, it uses resize2fs to do its work behind the scenes, anyway.
But, as always, when modifying a filesystem, a backup of important data is wise. At the very least, go out and get yourself a USB drive of a suitable size to store your data, and back it up before proceeding. Then you're covered if the worst happens. Or if you just want to start again.
Edit: I'd add that if your drive is more than 3-5 years old you should consider replacing it anyway.
Keep Calm and Carry On