It's likely your first attempt didn't have fully dry Future on it. How long did you wait? Future is good stuff and very cheap, but it's also very thick. I don't use it anymore for that reason... too many good hobby-specific alternatives are available. They're (much) more expensive by volume, of course, but you use so little it still amounts to pennies per model.
Current favorite is Alclad Aqua clear. You get the same shine, 'real glass look', and basecoat protection as Future, but it goes on much thinner and dries a lot faster.
I've also read that some modelers thin future to cut down on the coat thickness, but I've never tried that.