I don't think they fueled it up all the way. But I do thing the booster and maybe also starship itself is a little heavier than they plan to have it at the end.
*update* if you check the video just before launch (39:54), you can see that the fuel bars for both the booster and the ship is not 100% full: https://twitter.com/i/broadcasts/1OwxWYzDXjWGQ
*update* if you check the video just before launch (39:54), you can see that the fuel bars for both the booster and the ship is not 100% full: https://twitter.com/i/broadcasts/1OwxWYzDXjWGQ