Remember to work on developing intimate control of your sensitivity. For most players (but not all), they will find that if they can slowly train to play at a lower mouse sensitivity, they will be able to make shots more accurately. Again this takes time and practice.
I myself, play Widow at 2.65 in-game sensitivity at a 1600 mouse DPI with a scope reduction at 50%. Learn more on how to do this in my maximizing performance guide here:
Also, be sure to practice headshots a lot. This can be set up a bunch of Ana AI bots with headshot only turn on in a custom game skirmish. Some pro players will play games like OSU! and Aim Hero to practice as well.