The difference between 1.063 and 1.100 is 4 lbs of brown sugar in 5 gallons.
If you added about 4 lbs, then your sample was probably correct. If you added much less, then the wort was probably not mixed properly.
What yeast? With that much simple sugar, you could easily attenuate down to 1.010 or even much lower. If it goes down to 1.010, that will be about 12%, which will be hard work for a lot of yeasts.