If you have two objects in the outliner, then you might delete one (the "wrong" one ;-) ), if it is the same object you should mark the faces carefully, which are not belonging to the original. Hope its not too much work.
By the way, I strongly recommend to use the autosave - function, which can save every 10 minutes you work status. In case you messed up you model you should be able to go back to the last stage before this happened. I have several times that the original file was broken, fortunately i used this function. But don't forget to delete from time to time the autosaved files, because it will get quite big, keep some key work points only.