Some suggestions I wish I had when I first played scout:
1. Track your aim, don't flick. Focus on your crosshair and track your targets, don't try to flick to them and shoot.
2. Don't necessarily shoot as fast as the scattergun can shoot. Shoot only when crosshair and target line up, not every 0.6 seconds every time.
3. Easier said than done but try not to worry about performance. If you fight in situations when you have the advantage, hopefully that can relieve some pressure.
4. Get more frames
Not sure if any of these actually apply to you since I haven't seen gameplay.