[scottk_61]

I think you did well to communicate the deviation to your partner on the play you describe but the deviation was mandated by some bad mechanics on the PU's part.

Like Mike said, never run toward a catch, instead get as close as is reasonable to a 90 degree angle to the catch. Which in the play description would have put you around 3rd.
Persoanlly, with a dark field or a field with dark areas, I may have taken a step or two inside the foul line BUT NOT under normal lighting.
If you had been in the 3rd base area, you still would have been in place for a throw from the outfield for a play at 3rd if you needed to be.

I think you "done good" in that situation but that situarion wouldn't have occured if you had used the better mechanics that I am sure you know and would normally practice.