try setting the amount a bit higher or bundle all your input amounts through coin control, sent it to yrself, wait for confirmation and then do a mixing.
personally i would set the amount to at least 5 DRK ... to be on the safe side.
Yeah if you have say 10DRK total in your wallet but it's made up of a lot of tiny chunks then you'll need to consolidate it into one bigger lump by sending all the smaller amounts to one address.