SO EMBARRASSING!

Ok, first of all, it was really hard to think of a true and good story to tell you. The only fact I could remember is this one:
A long time ago, in the middle of summer vacation, when I was around 10 years old, one of my best friends invited me to spend a week in her flat. She used to live in a small apartment in Lago Norte and I was used to go there all the time. We were very close friends.
Anyway, one day we decided to make a joke with her mother and her sister. We went to a supermarket nearby and, when we got back home, my friend and I went upstairs quickly. We stayed in front of the lift and waited with our most scary and ugly face. We were going to scare her mum and her sister!
The elevator was coming to the third floor. We were both prepared to scream and laugh of their faces. And, all of a sudden, the elevator stopped and opened. We shouted: "BU!" with a very loud voice and started to imitate monsters or something like that. When we stopped doing that and looked at the horrified faces of the two men that were staring at us, we realized that we didn't know them and, obviously, they weren't my friend's mother and sister. One of the men was the manager of the condominium and the other was his friend.
We both blushed. We didn’t know what to do. We stayed quiet and staring at the floor. Finally, the two men laughed and went away. We were so embarrassed!