A good way to use up more scraps is to make the back from larger "scrappy" pieces. (All those FQs you don't have any idea why you bought and are just taking up room?) And if you have space, buy batting by the bolt when on sale at either JoAnn's or on-line. You can also buy muslin by the bolt and use it for backings.
But $20 for a quilt -- I think you did good!! And I'm sure your niece will just love it! :D :thumbup: :thumbup: