I accidentally dissolved faces when trying to simplify a mesh and trying to reduce the amount of faces. I’m not sure why I should have done, but essentially, I had subdivded my plane and now just needed one face at the bottom of. What is the correct step to create a new face in this empty space?
That sugggests maybe duplicate vertices somewhere, when you look in the status bar, does what you see tally up with what you are looknig at in terms of number of edges / vertices?
The error with grid fill is probably because of mismatched vertice number. You can try adding one edge loop on it. That of course will mess up your vertice density.
For this project, I would restart from beginning.