Go back to your PSP and undo the deselection and dsb, redo the DSB but this time click the mix twice. Deselct again and copy merged. In AS, right-click and paste after current frame.
Repeat this procedure once again, this time clicking three times on the mix.
Preview your animation in AS with the View Animation button. File - Save as "whatever you want to call your tag" (I assume you have proper settings for a .gif-file) and you're done!