I would definitely call and explain your situation to them. We had a similar situation where an unexpected expense came up and we weren't able to make the final payment at the 45 day mark. I called WDTC and they extended the final payment due date to accomodate our ability to pay. (We paid at the 35-ish day mark). Also, an FYI -- we had already paid about 75% of the package PRIOR to the 45 day mark, so they said they weren't concerned about not getting the remaining balance, since it was minimal compared to the full package price. But, again, I'd definitely recommend calling them and seeing if they can help you.
Good Luck!