Change 5-Star Rating to 3-Star

I would like to change a rating from 5-star to 3-star.  I created a picklist titled, "Grade," and the values are 1,2,3.  Then I have a formula field with the following, 

IMAGE( CASE(Grade__c, "1", "/img/samples/stars_100.gif", "2", "/img/samples/stars_200.gif", "3", "/img/samples/stars_300.gif", "/img/samples/stars_000.gif"), "WAS Rating")

Even though I only selected 1,2,3 for my picklist and 1,2,3 in the formula, the field still shows 5 available stars.  I want this to show 3 available stars.  Please let me know how I can do this.  

Thanks, 

Mike

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