Hi,
I agree that 3.38V are sufficient.
But for true resistor calculation you need to know the actual current. I´m not convinced that the circuit gives exact 1mA .. I rather think the OPAMP is saturated at it´s rail limit and the current is somwhere below 1.00mA.
--> Then the resistor calculation may be wrong.
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A simpler method is to just use an about appropriate resistor and measeure the voltage drop across this known resistor. Then you may calculate the true current.
Measure the voltage drop acrross the PT100 and calculate the exact resistance.
Klaus