Paula,
The process that you are using is based on accounting for WIP … since when you purchase the parts for a job they are not immediately “costed” since the sale has not been recorded (or possibly will not before the end of the accounting period, month)…. The setup you currently have probably nees to be looked at and corrected for your business flow …
There is a much better way to account for WIP and the parts should not be an “expense” but a COGS account so you can see your Gross Profit before Expenses …