Not really, no.
The Rom should only use about half of that.
Which is why it seems you have one backup hiding somewhere.
If I were you, I'd back up anything important to my computer.
Then I'd wipe everything and sideload or adb push the Rom.
That should clean everything up.
Then just put back what you need or want.
This is also dependent on how many apps you've restored or installed since loading the base Rom.
Some games and various apps data can be rather large.
Yeah, Google it, it's actually really easy.
Just a word of advice:
Place a working rom.zip on your device. (as a failsafe in case sideload or adb push doesn't work for you.)
Practice at least once, adb pushing or sideloading a rom, prior to wiping the device.
That way you can be sure you have the process working before you wipe the device.
This way, while practicing, if you have any troubles with adb or drivers, etc,..you'll still have at least one rom zip on your internal storage that you can flash back to until you get it working.
I don't wanna see you end up with no OS and no working method to get a rom back on the device.
(only reason you would have any issues would be due to adb drivers)
Once you know the process is working with your PC setup and drivers, then you can wipe and sideload for real...