How to know which reduction and oxidation reactions occurred?
Here, Fe(III) will be reduced to Fe(II), and Copper(0) will be oxidized to Cu(II).
The standard potential for Cu2+/Cu is +0.34 V, and for Fe3+/Fe2+ it is +0.77 V. 
Nernst's law gives the potentiels for a 0.5 M solution. It is +0.34 - 0.009 V = 0.33 V pour the Copper electrode, and 0.77 - 0.018 = 0.75 V for the Fe3+/Fe2+ electrode.
With this choice, you get nearly your results.
It you had chosen another system of half-reactions, you will get results which are far away from your measurements.