Tripple Cock-up

[JammyBStard]

I was been a bit clever two nights ago, I decided to use up all my old grains in a bit of a mash up; I concockted the following from all my left overs:

Batch Size: 10.00 L
Boil Volume: 12.55 L
Boil Time: 60 min
Brewhouse Efficiency: 71.60 %
Equipment: Jammys current

Taste Rating (50 possible points): 35.0

Ingredients Amount Item Type % or IBU
0.72 kg Pale Malt, Maris Otter (5.9 EBC) Grain 34.62 %
0.57 kg Wheat, Torrified (3.3 EBC) Grain 27.40 %
0.52 kg Brupaks Larger Malt (2 Row) UK (3.0 EBC) Grain 25.00 %
0.15 kg Oats, Flaked (2.0 EBC) Grain 7.21 %
0.12 kg Caramel/Crystal Malt - 20L (39.4 EBC) Grain 5.77 %
5.00 gm Magnum - Craftbrewer - Magnum hop pellets. USA - Crop '07 (AA 12.5%) [12.50 %] (60 min) Hops 15.7 IBU
5.00 gm B Saaz - Craft Brewer - hop flowers. NZ - Crop '08 (AA 8%) [8.00 %] (30 min) Hops 7.0 IBU
3.00 gm B Saaz - Craft Brewer - hop flowers. NZ - Crop '08 (AA 8%) [8.00 %] (15 min) Hops 2.7 IBU
0.13 tsp Irish Moss (Boil 10.0 min) Misc
1 Pkgs SafBrew Ale (DCL Yeast #S-33) Yeast-Ale

And I was thinking; just for fun I'd try a tripple decoction for the first time:

Mash Profile Name: Decoction Mash, Triple Mash Tun Weight: 2.07 kg
Mash Grain Weight: 2.08 kg Mash PH: 5.4 PH
Grain Temperature: 22.2 C Sparge Temperature: 75.6 C
Sparge Water: 6.45 L Adjust Temp for Equipment: FALSE

Name Description Step Temp Step Time
Acid Rest Add 8.68 L of water at 36.2 C 35.0 C 45 min
Protein Rest Decoct 2.32 L of mash and boil it 50.0 C 60 min
Saccharification Decoct 2.90 L of mash and boil it 64.4 C 15 min
Saccharification Decoct 1.57 L of mash and boil it 70.0 C 15 min For one reason or another I only hit 67' at this stage
Mash Out Heat to 75.6 C over 10 min 75.6 C 10 min

Mash Notes
Authentic Germany mash schedule. Attempt to draw decoction from the thickest portion of the mash. Some sources recommend that each decoction amount be given a 15 minute saccharification rest at 158 F (70 C) before boiling it. This I didn't do!

It all seemed to go pretty well untill I measured the OG and only hit 1.035

Beer Profile Estimated Original Gravity: 1.046 SG (1.044-1.052 SG)
Measured Original Gravity: 1.035 SG Here be the Problem
Estimated Final Gravity: 1.012 SG (1.008-1.012 SG)
Measured Final Gravity: 1.012 SG
Estimated Color: 9.3 EBC (3.9-7.9 EBC) Color [Color]
Bitterness: 25.4 IBU (10.0-20.0 IBU) Alpha Acid Units: 4.5 AAU
Estimated Alcohol by Volume: 4.39 % (4.50-5.50 %)
Actual Alcohol by Volume: 2.99 %
Actual Efficiency: 54.93 %
Actual Calories: 326 cal/l

So I tested the beer today as it seems to be finished primary fermentetion already, and its malty, hoppy but thin at only 3%
I'm not sure exactly want went wrong, the mash seemed to go well, perhaps I miss measured my grain, the mash did seem a little thin.

So how do i fix it? I've done some sums (Beer smith has done some sums) and 500g of Wheat spray malt into the mix should give me another 1.5% ABV
How would i go about adding the spray malt at this stage? chuck it in? boil it up? any advice would be apriciated.