If I press SHIFT "speed" increases

im still studying coding but i want to actually "see" my codes "work" so please help me

Code (csharp):

1.  
2. using UnityEngine;
3. using System.Collections;
4.  
5. public class HoverMotor2 : MonoBehaviour {
6.  
7.     public float speed = 90f;
8.     public float strafeSpeed = 90f;
9.     public float turnSpeed = 5f;
10.     public float hoverForce = 65f;
11.     public float hoverHeight = 3.5f;
12.     private float powerInput;
13.     private float turnInput;
14.     private float strafeInput;
15.     private Rigidbody carRigidbody;
16.  
17.  
18.     void Awake ()
19.     {
20.         carRigidbody = GetComponent <Rigidbody>();
21.     }
22.  
23.     void Update ()
24.     {
25.         powerInput = Input.GetAxis ("Vertical");
26.         turnInput = Input.GetAxis ("Horizontal");
27.         strafeInput = Input.GetAxis ("Strafe");
28.  
29.     }
30.  
31.  
32.     void FixedUpdate()
33.     {
34.         Ray ray = new Ray (transform.position, -transform.up);
35.         RaycastHit hit;
36.  
37.         if (Physics.Raycast(ray, out hit, hoverHeight))
38.         {
39.             float proportionalHeight = (hoverHeight - hit.distance) / hoverHeight;
40.             Vector3 appliedHoverForce = Vector3.up * proportionalHeight * hoverForce;
41.             carRigidbody.AddForce(appliedHoverForce, ForceMode.Acceleration);
42.         }
43.  
44.         carRigidbody.AddRelativeForce(strafeInput * strafeSpeed, 0f, powerInput * speed);
45.         carRigidbody.AddRelativeTorque(0f, turnInput * turnSpeed, 0f);
46.  
47.     }
48. }
49.  
50.