In this work we show the existence of closure domains in Fe0.8Ga0.2 thin films featuring a striped magnetic pattern and study the effect of the magnetic domain arrangement on the magnetotransport properties. By means of X-ray resonant magnetic scattering, we experimentally demonstrate the presence of such closure domains and also estimate their sizes and relative contribution to surface magnetization. Magnetotransport experiments show that the behavior of the magnetoresistance depends on the measurement geometry as well as on the temperature. When the electric current flows perpendicular to the stripe direction, the resistivity decreases when a magnetic field is applied along the stripe direction (negative magnetoresistance) in all the studied temperature range. Transport calculations in the Ohmic regime indicate that the main source is the anisotropic magnetoresistance. In the case of current flowing parallel to the stripe domains, the magnetoresistance changes sign, being positive at room temperature and negative at 100 K. An intrinsic magnetoresistant contribution arising from the domain walls appears as the most plausible explanation for the observed behavior. We have put in evidence the importance of using X-ray resonant magnetic scattering for the determination of thin-film properties related with the magnetic structure.