Very low wort level for AG Brew

I recently made my first all grain recipe. After the boil I had the SP perfectly where it should be, but I had around 4 gallons. I was aiming for a 5.5 gallon batch going into the primary.

This is my recipe and steps BeerSmith gave to me:
7 lbs Pale Malt (2 Row) US (2.0 SRM) Grain 1 65.1 %
3 lbs White Wheat Malt (2.4 SRM) Grain 2 27.9 %
12.0 oz Vienna Malt (3.5 SRM) Grain 3 7.0 %
0.60 oz Amarillo Gold [8.50 %] - Boil 60.0 min Hop 4 16.6 IBUs
0.50 oz Glacier [5.60 %] - Boil 15.0 min Hop 5 4.5 IBUs
1.00 tsp Irish Moss (Boil 10.0 mins) Fining 6 -
1.0 pkg American Ale (Wyeast Labs #1056) [124.21 ml] Yeast 7 -

14.4 qts@ 158° for mash. Sparge with 4.7 gal at 168°. That left me with over 6 gal of wort in my brewkettle. I forgot to take a preboil measure of SP. I did an iodine test after the mash and it did not change color, so I figured I was good to go for the sparge. How would I adjust the SG so I end up with the target volume instead of being a gallon or more shy?

When I racked from primary into bottles the SG was again, perfect with where the recipe said it should be. Thanks.

So you lost 2+ gallons during the boil. Did you do the boil outside? what is the diameter of your brew kettle?

I believe I lost more than that, but like I said the gravity was correct after the boil. I did boil outside, it was about 45° F that day. My brew kettle has a diameter of 12 inches.

I think my problem is more of not getting enough sugars from the mash.

Well your problem is two fold. First you had a to small preboil volume to end up with 5.5 gallons post boil. For this just increase your spare volume a little.
Secondly you gOt a lower efficiency than you expected. This is easy to fix just assume a lower efficiency in the future and use a little more base malt.