Hi Carol, are you still stuck on this level? If so, see if this tip helps you: http://candycrushsagaallhelp.blogspot.co.uk/search/label/Level%203137 the video has 20 moves not 18 and no center candies trapped.
It is because the boosters become what you need so if you need chocolate squares they become that if you need striped candy it becomes that you need to remove two pie wedge things one of the boosters can't become that it is stupid they used them I think they are just doing it to slow us down or make us spend money to get…