"make a straight line" is a correct and usable phrase in written English.
You could use it in contexts where you need to explain how to draw or construct something. For example, you could say, "Draw two straight lines from the top corners of the rectangle to make a cross."
In one sixth-grade class, Rashid was learning to make a straight line pushing pegs into a peg board.
He investigated the use of chance methods, photographing successive attempts to make a straight line or a square by throwing three or four colored balls in the air.
"To move through them you can never make a straight line, instead you have to move in between them and you make a new line.
Now Mr Bisignani gets everyone into one room to work out, say, the shortest route from London to Singapore, flying over borders to make a straight line, rather than the twists and turns of conventional airways.
Usually the carotid arteries make a straight line from where they take off from the aorta, the large vessel that leaves the heart, to where they deliver blood deep into the brain.
He instructed me what to do on the body, to make a line, an incision, to make a straight line, an incision from the throat to the end of the ribs.
Make a straight lines on your sketches, and erase your guidelines.
Tearing the canvas will make a straighter line than cutting it will.
When she sees what she wants, she makes a straight line for it, no apologies.
The liner's crew and passengers spotted a track advancing towards them across the flat sea, as if an invisible hand was making a straight line with white chalk across a blackboard.
But as Richards claims in his autobiography, Life!, it was the more sophisticated, worldly Linda who seduced him at a record release party: "She made a straight line for me.
