I go to college and work in PA and rent an apartment in PA,but am a resident of MD. I have been getting PA taxes taken out and no MD taxes, how do I fix this?

I rent an apartment in PA, and have a job in PA, my job never had me fill out a W4, and only used my local address for taxes so I have been just paying PA taxes. However, I have read that I am supposed to be paying MD taxes and not PA because of the reciprocal tax agreement. 1) is this correct? And if so, how do I get the money that PA took out back?