After Clark stops the three arrows from hitting Oliver, Oliver shoots Vortigan in his left shoulder. Directly after this, Vortigan is shown still having his bow drawn with his left arm pointing outwards, he then lowers his bow, to show the arrow in his left shoulder. From his previous position, Oliver's shot would have been impossible.
In the hospital Chloe tells Oliver that Lois was shot in the right shoulder with an arrow. However, in the next scene the x-ray shows the arrow in the left shoulder. Also, in the prior scene with Clark and Lois, her left arm is in a sling and left shoulder bandaged.