2 ?'s about the tripel I brewed Sunday

On Sunday I sat down and brewed what I'm calling Triple 10 Tripel (10-10-10 was the date). Its fermenting away nicely as I type this. First time I brewed a tripel though and was wondering what the purpose of the candi sugar is? Is it just an extra fermentable? Does it add some kind of flavor characteristic? Just not really sure what it does and was wondering.

Second thing is the directions in the kit say the SG should be about 1.070-1.075 for 5 gal. I bumped it up to 5.5 gal just which I normally do just to make up for any loss transferring and that sort of thing, and then added as an extra 1lb of corn sugar and still only got an SG of 1.070. I was hoping someone could tell me if that seems right, I thought it seemed low. Pertinent info about the brew below.

5.5 gal total volume
4.3 lbs dme
3.3 lbs lme
1 lb corn sugar
1.5 lbs candi sugar at 10 min
1.5 oz hops at 60min
.5 oz hops at 15 min
1 oz hops at 5 min
orange peel at 5 min

Yes, the candy sugar, if darker than clear, will add flavor.

The low OG reading was probably because you didn't mix the top-up water well enough with the wort. I woulnd't have added another lb of corn sugar to bump the OG. You should have just added more malt extract. The body of the beer may be a little thin since you used 2.5 lbs of sugar.