Tried editing the location of a new portal that is way off where it should be, but when I move the cursor to the correct location it just slides back to the current location, so I can't submit the correct location.
This is intended. A location edit via the app can only be done to a maximum of 25 meters. Everything above that and it snaps back.
You'll need to open a ticket at wayfarer.nianticlabs.com/help. Make sure you have the coordinates of the current and the correct location as well as some proof, such as a picture. Niantic will often move it within a few days.