Help with MS Excel S-Curve

This is a screen shot of my worksheet data. I got a review That said:

"Curve 1 is OK. Curve 2 needs to show the accumulative actual cost. The 2nd curve now seem to show the actual cost,
based on % completion, but it needs to be accumulative, which it is not.
In an accumulative curve, the curve will always go up when their is a payment and horizontal when there is no payment.
However, the curve can never go down."

Thanks for your reply!