Question

Suppose the thermometer is miscalibrated to read .3c higher than actual. does this error in calibrations result in the molar mass of the vapor in the flask being reported as too high or too low?

Answer 1

The answer to this question would be: too low

Molar mass would be determined by the number of mol and the mass of the object. Mass wouldn't be influenced by the temperature, but number of mol is. Using ideal gas formula of PV=nRT you can conlude that the amount of mol(n) is inversely related to the temperature (T).
If the temperature is higher than it supposed to be, then the amount of mol would be lower than it supposed to be.