Hi there kai,
Yes, I got the gist of your description so you on the right track. However, if I were you I would steer clear of repeating "have you ever" in the second sentence. Sometimes repetition can cause more confusion. Another recommendation would be to leave out describing in the 3rd person keep it direct as possible. Rather opt for:
"Have you ever been to a casino in Japan and noticed a machine with a lever? If you pull on this lever and manage to get three identical symbols you win a bunch of metal balls! That you can exchange for either cash or prizes".
Just my thoughts on it hope it helps..