Based on above it's hard to tell. Can you share your workbook with the community.
For sure a lot members will help out if they can examine your workbook.
You're going to want to change the "Calculate the difference along" from "Table (Across)" to "Specific Dimensions". Not having access to your dataset, I created a similar table using the Sample Superstore data. Since it looks like you have an older version of Tableau, check out the screenshots:
Let me know if this works for you.
Percent Difference from First.twb 195.9 KB