Good news: you don't have to recalibrate. SkyView only uses that initial number that you input to determine how many gallons to ask for per pour. In your case, it sounds like about 13 gallons is all that the sensor can measure before it tops out (this is common and expected. you should see either 12+ or 13+ on the gauge when you're full).
The fuel computer quantity needs to be set INDEPENDENTLY when you fill up. SkyView reminds you to set it when it sees a mis-match between the fuel computer values that you've inputted (minus what you've actually burned) and what the in-tank sensors are measuring upon startup. This is what happens when you fill the tanks.
When you see that message, you can press the "FULL" or "PRESET" (useful if you have aux tanks that you don't fill of tabs in your tanks for a partial fill), but you have to have set those FULL and PRESET values during setup/installation (full details in the installation guide at http://docs.dynonavionics.com, page 7-62 onward). If you don't have those values set, you can still spin in the quantity of fuel on board to make the fuel computer quantity correct. Note that if you have in-tank sensors that hit their peg early, you'd expect the in-tank and fuel comptuter quantity values to be slightly different when you're full. So in your case, when both tanks are full and you're finished adjusting the fuel comptuers: you'd expect to see something along the lines of
FUEL COMPUTER QUANTITY ADJUSTMENT: <will vary depending on how much you've filled>
CURRENT FUEL COMPUTER QUANTITY: 28 GALLONS (this is 14 * 2)
MEASURED FUEL (IN-TANK SENSORS): 25.8 GALLONS (this is 12.9 * 2, assuming both tanks calibrated exactly the same, which they probably didn't)
