Gun sway Logic Help Needed

hey thanks for viewing im not to sure not to describe the problem im having but here it is

 MoveOnX = Input.GetAxis("Mouse X") * Time.deltaTime * MaxMoveAmountX;
         MoveOnY = Input.GetAxis("Mouse Y") * Time.deltaTime * MaxMoveAmountY;
 
 
 
         //***** SHOOTING *****\\
         if (Input.GetButton("Fire1") && canFire) 
         {
             if (tillNextFire <= Time.time)
             {
                 tillNextFire = Time.time + fireRate;
 
                 //Canculates the random target recoil
                 targetRotationalRecoil += new Vector3(-RotationalRecoil.x, Random.Range(-RotationalRecoil.y, RotationalRecoil.y));// calculates the target recoil
                 targetPositionalRecoil += new Vector3(Random.Range(-KickBackRecoil.x, KickBackRecoil.x), Random.Range(0, KickBackRecoil.y), -KickBackRecoil.z);
                 ///////SHOOT///////
                 
             }
         }
 
 
 
 
         //******* AIMING *******\\
         if (Input.GetButton("Fire2")) 
         {
             holdRacio = Mathf.Lerp(holdRacio, 0, speedToAim * Time.deltaTime);
         }else{
             holdRacio = Mathf.Lerp(holdRacio, 1, speedToAim * Time.deltaTime);
         }
         currentAimPosition = new Vector3(Origin.x * holdRacio, Origin.y * holdRacio, Origin.z * holdRacio);
 
         // ******** GUN SWAY / MOVEMENT *******\\
         NewGunPos = new Vector3(Origin.x + MoveOnX, Origin.y + MoveOnY, Origin.z);
         movementToAdd = Vector3.Lerp(transform.localPosition, NewGunPos, MoveSpeed * Time.deltaTime);
 
 
 
 
 
         targetRotationalRecoil = Vector3.Lerp(targetRotationalRecoil, Vector3.zero, speedToOrigin);
         currentRotationalRecoil = Vector3.Lerp(currentRotationalRecoil, targetRotationalRecoil, speedToRecoil);
         targetPositionalRecoil = Vector3.Lerp(targetPositionalRecoil, Vector3.zero, speedToOrigin);
         currentPositionalRecoil = Vector3.Lerp(currentPositionalRecoil, targetPositionalRecoil, speedToRecoil);
 
 
         
 
         
         
         
 
         
         //transform.localPosition =  movementToAdd;
         transform.localPosition = currentPositionalRecoil + currentAimPosition;
         transform.localEulerAngles = new Vector3(currentRotationalRecoil.x, currentRotationalRecoil.y, currentRotationalRecoil.z);

this is a few lines of my code where im having troble the recoil is working properly and the aiming but when i try to add gun sway when you move your mouse the tutorial i watched wants me to transform.localposition = movementToAdd

where as i need to do transform.localposition += movementToAdd

so i can add it to the line

transform.localPosition = currentPositionalRecoil + currentAimPosition;

to make it

transform.localPosition = currentPositionalRecoil + currentAimPosition + movementToAdd;

any help would be awesome

thanks ~Scott