Error CS0101 in C#

Started coding a door script for an animation that happens when the door's box collider is triggered. I figured I would watch a tutorial video on it (it was this video: https://www.youtube.com/watch?v=iKWJBgFCDWU) and follow along since I did not know how to do it initially. Turns out, I did not do it right, and even looking through and copying EXACTLY what the video stated, I still got an error message. Here is the code that I wrote:

 public class Door : MonoBehaviour {

 private Animator _animator;

 // Use this for initialization
 void Start () {
     _animator = GetComponent<Animator>();
 }

 void OnTriggerEnter(Collider other)
 {
     if(other.tag == "Player")
     {
         GetComponent<Animator>().SetBool("Open", true);
     } 
   
   }
 }

This code is producing the error: Door.cs(1,10): error CS0101: The namespace 'global::' already contains a definition for 'Door'

I have no idea what this means. If somebody could potentially figure out this error (since I cannot go into play mode until this is solved) or maybe give me a new video that might not produce this error, then I would be very grateful.