Lock transform rotation on Y axis

Hello,

I have a script where you can climb up walls and ceilings with a guy 2D.

But sometimes he deviates off the course.

How can i lock his rotation? The scripts is pretty complicated.

 private Quaternion GetMagneticRotation()
 {
     closestSphereCastHit = null;

     if (Physics.SphereCast(transform.position, collider.radius, -transform.up + transform.forward, out RaycastHit hitForward, SPHERECAST_DISTANCE, RayCastLayerMask))
         closestSphereCastHit = hitForward;

     if (Physics.SphereCast(transform.position, collider.radius, -transform.up, out RaycastHit hitDown, SPHERECAST_DISTANCE, RayCastLayerMask))
     {
         if (!closestSphereCastHit.HasValue || closestSphereCastHit.Value.distance > hitDown.distance)
             closestSphereCastHit = hitDown;
     }

     if (Physics.SphereCast(transform.position, collider.radius, -transform.up - transform.forward, out RaycastHit hitBack, SPHERECAST_DISTANCE, RayCastLayerMask))
     {
         if (!closestSphereCastHit.HasValue || closestSphereCastHit.Value.distance > hitBack.distance)
             closestSphereCastHit = hitBack;
     }

     var normal = closestSphereCastHit?.normal ?? Vector3.zero;

     var lookRot = Quaternion.LookRotation(Vector3.Cross(transform.right, normal), normal);
     return lookRot;
 }

 private void MagneticRotate()
 {
     var stickedRotation = GetMagneticRotation();

     if (Time.time > lastTimeWooshed + 0.5f && stickedRotation != lastStickedRotation && Time.time > 1f)
     {
         WooshSound.Play();
         lastTimeWooshed = Time.time;
     }

     var desRot = Quaternion.Slerp(transform.rotation, stickedRotation, Time.fixedDeltaTime * currentMagneticRotationSpeed);
     transform.rotation = desRot;

     //transform.Rotate(new Vector3(0f, 1f, 0f), 1f);

     lastStickedRotation = stickedRotation;
 }