Nernst equation and equilibrium potential
The Nernst equation should be:

RT/(zF)*ln(Out/In) = 2.3 RT/(zF)*log10(Out/In)

You substituted for 2.3 RT/F (approximately 60 or 61 mV: use 60 because your instructor asked you to), but forgot about z. Calcium is divalent (and positive) so for calcium z=2. Substitute this and you can see how you get your answer. 

(Also note the "out/in" which is how you get negative numbers when z is positive and out &lt; in )