mathf.clamp doesn't clamps

mathf.clamp doesn’t clamps my value between 0 & 1 i.e it goes beyond 1 upto 1.2

start = Mathf.Clamp (start,0,1);


			if(Input.touchCount > 0 ) 

				start += Time.deltaTime*3;
				
			if (Input.touchCount == 0 )
				start -= Time.deltaTime*3;

You’re adding after you clamp.