Hehe.... got a good one for ya...
Just added another fuel up. Now it says once a week. Hehe
Lets just wait and see how it works out for a few months. Don't want to waste your time. Especially if all I need is more data input.

Question, when you buy a new car and start off, how are you supposed to account for this? It seems to me the first tank while technically NOT filled by me, came with the car and should be accounted for. Did I mess up? My total mileage seems to be low. HELP...

Depends on how you have selected to track your distance per tank.

Since you get the car with an unknown amount of fuel in it, you need to do an initial fill up to get a start point in which you know the tank is full. How you track this first fill on Fuelly depends on how you are tracking the tank distance.

By odometer, fill up the tank, and put an entry for it in your Fuelly log. This is to establish the start point, with full tank and initial odometer reading, for tracking your fuel economy. There won't be a fuel economy figure calculated for this fill.

By trip odometer, Just fill up and reset the trip meter. You put the first Fuelly entry in on the second fill up.

Car came w/ full tank of gas. Since I know that and the mileage, is it too late to add to current fuelly stats?

It may not have been completely full though, you can get much more, in some cases gallons of extra fuel in if you brim the tank. Unless you did this, then you first tank is going to seem worse as it will assume you used more fuel than you actually did. Your first fuel up should be the miles just driven, but measured using the fuel you just put in. I don't believe in "initial fills" or the like.

My total average on fuel ups is finally straightened out.
I can only rationalize it was lack of data. I know...I know... but don't argue with the computer....rationalize.