Skirt Lifter Imperial Hefeweiss

I brewed Bub's Skirt Lifter Imperial Hefeweiss. But I anticipated an OG of 1072, and got 1088! What??

ProMash Brewing Session Printout
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Brewing Date: Sunday February 03, 2008
Head Brewer: Jeff
Recipe: Skirt lifter Imperial Hefeweiss extract
Recipe Specifics
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Batch Size (GAL): 5.00 Wort Size (GAL): 5.00
Total Extract (LBS): 12.00
Anticipated OG: 1.072
Anticipated SRM: 3.6
Anticipated IBU: 17.9
Wort Boil Time: 60 Minutes
Actual OG: 1.086
Grain/Extract/Sugar
% Amount Name Origin Gravity SRM
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100.0 12.00 lbs. Wheat Malt Extract North America 1.030 2*

Hops
Amount Name Form Alpha IBU Boil Time
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0.33 oz. Horizon Pellet 10.90 16.0 60 min.
0.80 oz. Argentine Cascade Pellet 3.20 1.9 5 min.
0.20 oz. Argentine Cascade Pellet 3.20 0.0 0 min.
Yeast
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2 White Labs WLP300 Hefewizen Ale
Mash Notes
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Brought 1.5 gallons water to the boil. Add 12 lbs (1 gal) extract, and filled kettle to 3 gallons before bringing to a boil. I boiled 5 minutes before "starting" the boil. Put 1/2 bag of ice in sink and set kettle in it.