You really need to fix up[ your indentation. Some of your lines are indented 4-spaces, some three, and some 2. Even if you remove the extraneous semicolon and add the proper close for the if-block, you will still have unmatched braces. Indent everything exactly the same number of spaces and you should find the problem.
When you have got the indentation and formatting right: why are you declaring the result as a double? Fibonacci numbers are integers. You can probably use an int, but for results ≥ 2³¹ use longs or BigIntegers.