Non-zero output from a LM741 in a differential configuration
The input offset voltage for the LM741, at the gain you are talking about, would by itself be enough to cause more than 1V of output offset. Also, differential amplifiers are very sensitive to resistor tolerance and matching. Even if you replace the LM741 with a opamp that has a few uV of offset voltage, without also changing the resistors to be matching dividers of very high precision, the output will still have too much offset. 

It would be best to use an instrumentation amplifier in this case. Something like a AD623 would probably work.