Is there any way to go back to the original RAW on lightroom if you have messed it up?
Just to clarify what happens:
Lightroom's "Library" function is to act as a database for your images.
So when you import them, you tell Lightroom where you want the original files to be stored.
You can also tell it to make a back-up copy in another location at the time of import. So you can have them on your hard disk, with a copy of all the images on an external drive.
So long as you only use lightroom for this, and not windows explorer for example, Lightroom always knows where your images are.
When you open an imported image into the "Develop" module in Lightroom, the image opens up, and you can adjust to your heart's content.
You could, for example make 6 "virtual copies" of an image, and process it in 6 different ways.
When you make any changes to an image, the original doesn't actually get changed at all. Instead, Lightroom keeps track of any changes you make in a small "sidecar " file, which it also stores with the image info. So when you re-open the image in the future, Lightroom opens the image, then reads the sidecar file, and applies any changes it recorded to the image.
So at any time you can not only undo the changes one by one to eventually end up with the original, but you can press a reset button, to undo everything if you really screw things up.
Hope this doesn't sound patronising, it certainly is not intended to be, instead I hope it helps with your understanding.
Cheers,
Gary