I do get big and small colonies at times. And I believe it is due to how you spread your dilution on the plates. But it is okay. It is very simply to pick small colonies. Here is one trick. Buy some toothpicks and place them in a beaker. Cover it with aluminium and send it for autoclaving. AFter that, you can always pick your tiny colonies with the toothpick and drink the toothpick into your culture tube containing LB broth and the appropriate antibiotics!
Instead of tooth picks what about the pipette tips?