drifting

Hello,
Is there anyway that I can stop the plane from drifting when I have on true airspeed because it drifts very far away from my flight plane route also what do I judge my speed on what the GPS says or the main panel?
thank you
Is there anyway that I can stop the plane from drifting when I have on true airspeed because it drifts very far away from my flight plane route also what do I judge my speed on what the GPS says or the main panel?
thank you