So, to get an average of the data from my excel-sheet, I can only have two fuel-ups? And what do i do about the volume of fuel, what do i put in? Or can i have 40-ish fuel-ups, with odometer readings at both ends, and then just have blank odometer-readings?
That's just it—the data you have is not going to work here at Fuelly. I'm sorry about that, but I don't think there's any way around it.
You might want to summarize your current fuel economy findings from your spreadsheet and enter it as a note here at Fuelly. That will tell others what you've learned from your personal tracking. Other than that, I don't think there's a good way to use your data here at Fuelly.