Hey guys, I was wondering, is it safe to lose 15 - 20 lbs in 2 months? My best friend is getting married soon and I'm going to be her maid of honor

. I look ok in everyday clothes, but everytime I get into a dress it seems like my stomach just wants to hang out all over the place. Everyone thinks I've got great looking legs and arms, but I just can't seem to shake off that belly.
I've lost about 10 lbs already (was 167, now 157 at 5 ft. 8 in. tall), but I'd like to be about 145 -140. I exercise 6 times a week, between 2 and 3 hours a day. Most of that is walking, with 15 min on a stair master and 30-45 mins lifting weights. I think it's my diet that's the problem. I talked to my nutritionist (sp?) and she said, based on the amount of activity I do, I could have up to 2,100 cal and 350 carbs a day max. That seems like alot to me, so I was thinking maybe 1,800 cal and up to 200 carbs a a day. Does that sound ok?
Anyways, thanks in advance for all the tips.