What is this movie?(please help!)?!

its an older movie, been out a LONG time!. its something like treasure island or something!. i remember there is a tree that has bubble gum pizza!. then there is a mermaid with blond hair and a blue tail!. towards the end a bunch of people including a boy are in a place and the walls are closing!. the boy is dragging the mermaid out and the wall is slowly moving to squish them!. then at the end the people are carrying the mermaid on a rug and they roll her into the sea again!.!.!.please help me figure this out!. it is driving me insane to be able to figure this out!Www@Enter-QA@Com

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