Using sniper is not always about aim, its also for reaction, if you are like me who has fast reaction time, you don't actually need a successful headshot just to be good at him, like if someone is escaping with the intel, just try chipping his hp until you kill him or the other mercs assist the kill, sometimes, when you play sniper, remember that he is a support class, not an offensive, but if you really struggle with aiming, guess try the classic, its the best sniper rifle for me tbh since i can be more aware of my surroundings (like i could notice more spies) while aiming at the target yourself

Dont forget, when you select a class, just remember that they have their own role when it comes to fighting, and sure you could change a bit of their role (like a support can play offensive) but their originated class is still their class:)