Luke is pretty consistently shown to be ambidextrous (having the ability to use both hands without favouring one) throughout the original trilogy film series.
In A New Hope he totes a gun and shoots with his left hand while on the Death Star.
He operates a control panel with his right hand
He ladles food onto his plate with his left and then passes a heavy jug from his right hand to his left to pour.
He uses a screwdriver with his right hand.
He handles the lightsaber with his right hand.
He favours his right hand for throwing a grenade in Empire Strikes Back.
He eats with his right hand in the swamps of Dagobah, as well as pulling a gun with his right.
But then eats with his left hand a few minutes later.
He favours his right hand for reaching out with the Force.
He totes his gun in his right hand on Cloud City.
He throws a skull with his left hand in Return of the Jedi.
He salutes Jabba and catches his lightsaber with left hand.
He calls the lightsaber to his right hand and fights almost exclusively with his right.
It's not clear if this was an intentional directorial choice, a goof (reversed plates meant that Fett's antenna swapped sides repeatedly during the Skiff scene and Luke's lightsaber would repeatedly jump from his left to his right hip, for example) or whether Lucas simply didn't notice or care that his main actor (who's left-handed in real life) was using his hands interchangeably.