"worse-case scenario" is also how i try to think in order to get myself to cut up the lovely fabric i have.
about getting started...how 'bout spending a little more time with the inspiration quilt. look at it. touch it. talk about it with the store staff. perhaps that might put some of your fears to rest. best-case scenario is that the store will still have the fabric if you feel you have made a "mistake" and have to purchase more.