Missed my OG

I made my second attempt at AG brewing this weekend and I missed my OG pretty badly. I was making a mint chocolate stout (recipe was from this webstie) It was supposed to be 1.060 and I got 1.045. I'm trying to trouble shoot what I did wrong. I mashed at 152 degrees for 60 min with 17.81 qts of water and I sparged at 168 for 15 min with 24.5 qts of water. I had 12.25 pounds of grain. Mash went well and I thought the sparge went well also, but next is where I ran into problems (I think). When I was draining the sparge I didn't have enough room in my boil kettle to hold all the liquid safely. So I ended up not using about 2 qts of the sparge water. I then boiled for 60 min and ended up with almost 7 gallons of liquid with 5.5 gal being my target. I could only fit about 6 gallons safely in my fermenter ( I knew if I went and higher than 6 gal. I would be asking for trouble.) Should I have boiled longer to get my volume down to the 5.5 gal? Would boiling longer have effected the flavor of the beer?
As an aside the hydrometer sample tastes great and I can't wait to drink it once its done, but I'm curious where I went wrong.

Your OG was off because you didn't boil off enough. The same amount of sugars are in your 7 gallons that should have been concentrated into 5.5...... Next time you brew your gonna have to use alot less water from the get/go......(using less in the sparge...) It takes a while to get your system volumes down.

how big is your kettle? Sounds like it is about an 8 gallon kettle?

Let's assume that you went to boil with 8 gallons and ended up with 7 gallons after 60 minutes. This means that you boiled off about 12.5% in one hour.

Next time, if you want to end up with 5.5 gallons after 1 hour, you should shoot for about 6.2 gallons pre boil (5.5 x .125 + 5.5). There are calculators online to help you with your mash and sparge calculations such as: http://www.brew365.com/mash_sparge_water_calculator.php

Keep in mind for higher gravity beers, you must mash and sparge with more water to get the efficiency that you're after. To accomidate the extra water, you will need to boil longer - like 90 minutes or so.

My method is to follow the calculator, with 15 minutes left in my boil, I put my measuring stick into my wort to see how many gallons I have. Then I adjust my btu's to either more or less aggressively boil so that I end up w/ the correct amount of wort.

Will a longer boil effect my flavor at all? Also if I end up with to much sparge water would it make sense to boil off some of my wort and add the extra sparge after I make room in my boil kettle. I Definitely need to make a measuring stick. Much easier than guesstimating.

You should use the calculator. If you do that, you wont end up w/ too much sparge water - you'll know exactly how much you are going to have before you start to brew.

If you do a longer boil, just make sure that you add the hops at the right time. For instance, if you do a 90 minute boil, your first hop addition will likely be at 60 minutes. So you will boil for 1/2 an hour, then begin your hop additions.

As far as I know, a longer boil will not effect the flavor.

Got it. It looks like I was about a gallon off from the start (Between Mash and Sparge). So if I take that into effect I probably would have been closer to 6 gallons after the boil. I'll try reducing the initial water next time and hopefully I will end up closer.

yep, I show the same thing. Does your kettle hold 8 gallons?

I have to double check, but I think its an 8.5. Which would work just fine if I reduced my water by 1 gallon. Do you think its worth is to buy a 10 gallon SS pot? Or should I go with my 8.5 for a while longer?

8.5 should work fine for 5 gallon brews. My typical wort onto the boiler is 6.5 or 7 gallons which I boil down to 5.5

Look into fermcaps, they will reduce the foam in your boil.