The Eu-XFEL, a 3.4 km long free electron laser situated in Hamburg, Germany was commissioned in 2017, and has since been at the forefront of cutting edge technologies. The short laser-like X-ray pulses produced within the facility can be used to film ultrafast phenomena such as the formation or breakup of chemical bonds, research the composition and structure of complex biomolecules on the atomic scale, and can even be used to study matter under extreme conditions. Since its commissioning, a concern has been raised regarding the demagnetization of the permanent magnets present in the undulator system as a result of stray radiation. To monitor this, Gafchromic EBT-3 films along with other dosimetric tools have been installed at various points along the beamline to monitor radiation induced damages and predict the lifetime of the undulator system. This work focuses on optimizing the calibration of Gafchromic EBT-3 films for accurate estimations of the unwanted dose absorbed in the magnetic material, and was achieved by increasing the amount of calibration measurements and segmenting the measurements, in turn performing the calibration in parts. The results show that calibrating the EBT-3 films according to the proposed method can accurately estimate unknown doses up to 52 Gy.