Why is the amount raised for a fundraiser different in GivePanel than it is on Facebook?
There is usually a 48-hour delay from when a donation is made to when it will appear in Facebook's Multi-Day Transaction Reports. This is why the amount shown in GivePanel can be different from the amount shown on a Fundraisers Page on Facebook.
If you're confident the reason isn't because of the 48-hour delay, one other thing to check is that you didn't miss any data in your uploads. We've seen a few times organizations unsure why they are seeing a difference between GivePanel and Facebook and on many occasion it has been because there were a few days in the month that didn't have data uploaded for.