The Padlocked Chest

Yesterday in my Writing for Young People class at Uni we were given a task, just to get us writing. We were given a short beginning to a story and had to continue it. This is what I was given:

I sneaked into the old, abandoned house at the end of the street. I was surprised to find a small, padlocked treasure chest on a dresser in an upstairs bedroom. There was a note that said, "Do not open. EVER!" I also noticed a small key hanging on the wall. I tried the key in the padlock. It was a perfect fit.

Maybe you have some idea about how you would continue this story, but here is what I wrote:

I paused. My heart began to beat quicker and my hand, which was still holding the key, began to shake. Was I really going to do this? I couldn't very well not now. I glanced about, breathed in slowly and then, as quickly as I could, turned the key and flipped the lid open.
     An intense amount of noise hit my ears and at the same moment I felt myself get tipped forward, going head first into the chest. That was ridiculous though, I was was much to big to fit into such a small chest. As I fell, however, I realised that I was shrinking rapidly, until I landed with a thud on on the bottom. The lid slammed shut above me and plunged the inside into darkness.
     I lay still for a moment, dazed from the fall and then I heard a click and a chink of light appeared above me. The key had been removed from the hole.
     'Hello,' said a voice.
     I jumped and turned around on the spot. In the small amount of light I made out a whole crowd of people. Slowly they gathered around me.
     'Hello,' the man said again, 'what's your name?'
     I was still very surprised and confused, but I managed to say, 'Edward.'
     'Welcome Edward,' said the man, 'my name is Robert.'
     'Do you live here?' I asked.
     Robert looked at the others. 'You could say that, yes, but we haven't always. We came here the same way you did. I have been here for eighteen years. I was about your age when I unlocked the chest.'
     'Can't you get out?' I said.
     'To get out through the lid is impossible unless it is unlocked, but it is only unlocked when someone like yourself comes along. We tried to warn you by shouting but it never works.'
     That explained the noise, I thought. 'So there's no other way out?' I questioned.
     'Well,' said Robert, 'there is a small door, over in that corner, but it has another sign with it.'
     I peered through the gloom and made out the door and the sign above it that said, "Do not open. EVER!" 'That's the same sign which is on this chest,' I commented.
     'Yes,' said the man sadly.
     'So, why has no-one opened the door?'
     'We made the mistake once, why would we make it again?' said a woman.
     'Correct,' said Robert, 'we have learnt our lesson.'
     'No!' I said, 'we should open it.'
     'Shhh, now,' said Robert, 'you've had a big fall, don't get upset.'
     'This is ridiculous,' I said, standing up. Then I raced to the door and grabbed the key.
     'No! Don't!' screamed the people, but too late, I turned the key and swung the door wide open.