"You miss 100% of the shots you don't take"
I think my accuracy on Ana is around 13%. I find myself rarely zooming in unless I need to shoot an enemy Pharah out of the air. You obviously can't heal people through walls so they understand to come to you for heals.
The key to improving are her other abilities. Get better at using the grenade for heals and debuff. Use it often when starting out. When your aim gets more reliable, you can hold it for when you need it. Everyone agrees that a godlike Ana will get clutch darts on dangerous threats.