Is this worth getting fired over?

At work I'm responsible for dealing with a lot of money. My boss asked me to put £1000 pounds aside from the days earnings , so in an envelope I put 10 10 pound notes, labelled it £1000 and put it in the safe. I was ill that day so things were not registering, it did not register that I'd put £100 rather than £1000. Two other people know the key to the safe. They always just ram things in there and make a mess inside. The next morning I again opened the envelope and counted 10 £10 notes just to make sure it was all in there. Still did not register.

The next evening my boss called to ask where the envelope was. I told him it was upright in the safe, labelled. He couldnt find it anywhere. Someone had stolen it. He called again the next day and it registered that it was £100. I told him this, and he got really annoyed that he had to go to the store again and that he hadnt been feeling well. And if he'd known it was only £100 he wouldnt have stressed so much. My point is, if the envelope had not been stolen, he would have seen it was £100 and not £1000. And it's not my fault the other guys are so messy. Is what I've done really bad? He could just take the £900 from his account. That;s where it went.