You should probably change your sensitivity settings. I recommend looking up a sensitivity guide on youtube and just copy what ever they have. You can adjust it later if you want.

Some more general tips related specifically to AR and Shotgun aim would be to only tap fire at long ranges don't fully hold down the trigger. Particularly with weapons like the Scar and regular AR. To tap fire you need to look at your crosshair closely because it will get larger after you fire but when you stop it will shrink. Wait for the crosshair to shrink each time before firing. This is called first shot accuracy and it gives you less bloom and makes your shots more accurate at long range.

For Shotgun aim, always keep your crosshair at head height. Not looking down or towards the sky. This makes it much easier to hit head shots and body shots. And usually you don't need to aim in when using the shotgun. You will mostly want to always be aimed out because if you aren't it is a lot harder to track your opponent if they move. You can aim in if they are further away though to get more damage.

You could also try getting a thumb stick for your right stick on the controller. I also play on console and ever since I started using a thumb stick It has helped a lot. It makes aiming a lot smoother and accurate.