Assuming you are already there, going up to the Whitney Trail is probably easier, with less people, from Guitar Lake. How you would get stuck on the "wrong side" is a item of wonder to me. Did you plan to cross Trail Crest and drop down to Guitar Lake, then summit from there? That's a real grunt, if you don't mind.
I enjoyed my ascent from a small lake on the Muir Trail about there, then carried all my gear up to stash it all at the junction, bag Whitney, then out to the Portal, starting at South Lake (100 miles). Best time of my life till then.