brother these spray cans are not that tough to stand the tough conditions that a fuel tank of bike goes through. Paint on fuel tanks of bikes is sprayed thick with several coats and then baked to make it hard.
Repainting a bike involves removing previous paint, denting and very neat sanding to make the pre paint surface smooth, again several coats of paint and baking.
Spray paint in a can wont give you permanent shine and may come off very easily with the petrol spilled while re filling your bike.
recommendation! dont go for spray paint its useless, repainting by professional painter isnt so expensive and may be done within 1000 - 1200.