M300+P1 camera not keeping straight on mapping missions

I've been doing flight plans recently with our M300 and P1 camera, using Map Pilot Elite on smart remote control app. 

When creating the plan the flight path shows straight lines but after the aircraft take off it won't follow the plan laid off and start takin curved paths resulting in not covering 100% of the survey area.

Any suggestions on what may I be doing wrong? 

Thanks