Beersmith IBU problem

Ok, so i plugged the following recipe in to beersmith and it's calculating 35 IBU. But the recipe claims 65. I can get to 65 if i double the 75min warrior hop addition to 2.0 ounces instead of 1, but if im doing this all wrong then I don't want to overdo it.

Widmer Brewing Co.W-10 Pitch Black IPA Clone
5 gallons/19 L, extract with grains; OG = 1.064 FG = 1.014; IBU = 65;
SRM = 30; ABV = 6.5%

Ingredients:
7.75 lbs. (3.5 kg) Briess light, unhopped, liquid malt extract
1.5 lbs. (0.68 kg) caramel malt (10 °L)
12 oz. (0.34 kg) Weyermann dehusked Carafa® II malt (450 °L)
10 oz. (0.28 kg) Briess special roast malt (50 °L)
16 AAU Warrior hops (75 mins) (1.0 oz./28 g of 16% alpha acid)
1.4 AAU Cascade hops (2 mins) (0.25 oz./7.1 g of 5.8% alpha acid)
12 AAU Warrior hops (2 mins) (0.75 oz./21 g of 16 % alpha acid)
0.25 oz. (7.1 g) Warrior hops (dry hops)
0.50 oz. (14 g) Cascade hops (dry hops)
½ tsp. yeast nutrient (15 mins)
½ tsp. Irish moss (30 mins)
White Labs WLP001 (California Ale), Wyeast 1056 (American Ale) or
Fermentis US-05 yeast

Any ideas on how I screwed this up? Or is it some kind of misprint?

make sure you have pellet or whole correctly selected, and make sure it's using the right formula like rager, tinseth, etc. That should help a bit

Are you adding at least 1/2 of your extract at or near the end of the boil? I like to do that, as it keeps the flavor better (less maillard reactions and 'extract-y' and carmelly flavors) and keeps the color light. In addition, you'll see your calculated IBUs skyrocket!

I'd input two extract additions into Beersmith. For one, use 2.75 pounds LME. Then for the second, use 5 pounds of LME but check the box in the screen for "boil extract for ____ minutes" and add it near 10 minutes left, so you can bring it back to a boil before adding the latest hops. Just put 10 minutes in there, and you'll be very close.

When I get back home in a few days, I'll definitly give that a try. I'm trying to stay away from just reading recipes out of a magazine and getting down to the nitty gritty. It's a steep curve!

Thanks for the tip!

Wow, I added 2.0 LBS of the LME at 60mins, and 5.5 at 15 mins, and it brought the IBU up to 60! What a difference! Thanks!