I make divinity to sell every holiday season, so I have a recipe that works great. The only time there is a problem is:

If the syrup isn't cooked to at least 260 degrees or a little tad bit over; or
The mixture isn't beaten enough.

I have a big old Kitchenaid mixer which really gets with it. I burned up several hand mixers trying to beat divinity and decided it would be cheaper in the long run to spring for a Kitchenaid. I don't know how people used to beat it by hand. I have done it...once, but that was enough for me! It will definitely lose its gloss and pull the mixer down when it is ready. Don't give up! Give it another try. I'm sharing my recipe, although I doubt it's much different than the one you used.

DIVINITY

2 1/2 c. sugar
1/2 c. water
1/2 c. white corn syrup

Combine above ingredients in a heavy saucepan. Stirring frequently, bring to a boil. Cover and let steam for a minute or two to dissolve any sugar crystals which may be clinging to the side of the pan. Remove cover and place candy thermometer in pan. Boil without stirring to 260 degrees. Remove from heat.
While the syrup is cooking, place two egg whites in a large mixing bowl. Add 1 tsp. of vanilla. Beat until the mixture forms stiff peaks. After syrup is cooked, slowly add hot syrup to the egg whites while constantly beating at a high speed. Continue beating until all the syrup is added and until the mixture loses its gloss and gets very stiff. Drop by spoonsful onto waxed paper or parchment paper. Or you may spread it into a greased 11x7 pan and cut into squares.