Beer Volume

I am in the process of brewing my first batch of beer ever (YAY!!). When I did the initial brew, I boiled 2 gallons of water first and set it aside. I then did the actual brew boil with 3.5 gallons in a 5 gallon pot. I guess I boiled off a full gallon in my hour long brew. I had premarked the carboy at 5 gallons exactly. So when I put the wort in the 6 gallon carboy for primary fermentation, it only reached about the 4.5 gallon mark. Not having any other sterilized water, I just pitched the yeast and capped it (at 77degrees as specified). My question is: Is having a 4.5 gallon batch with 5 gallons worth of ingredients going to have a detrimental effect on the taste of my beer?

I'm trying to RDWHAHB as much as possible, but also want to learn the intricacies of making a good brew at the same time. Any advice or insight will help.

Detrimental? Unlikely. It will be 10% stronger, with a richer flavor you may or may not detect. The biggest drawback is the 5 bottles you will be missing. Just enjoy it, there's so much to learn from your early batches and this is just one of those lessons.

It might be a little more concentrated, but i doubt you will be able to tell any difference!

What kind of beer is it? 77* seems high for ale and low for saison

next time buy a gallon or two of bottled water. i've always topped off with it and never had an infection.... from the water.

Blackguard Brewing - Its a Pale Ale. The directions said to pitch at 77, but the yeast says to primary ferment between 65-75, so I've been keeping it in my basement at around 68-72. Check it this morning, fermentation is definitely slowing but I've probably got at least a couple more days in primary before moving to secondary.

When I move it to secondary fermentation, is that too late to add a little bit of boiled water to bring the volume up? Or should I just let it sit at 4.5 gallons?

I think if you look into it moving to a secondary is considered unneccasary and most conclude that a long primary is better for the beer. I usually do a 3 week or 1 month primary, and if I am dry hopping I do so at the tail end of the primary for however many days and then bottle. The less you can move the beer from vessel to vessel the better.

Does anyone think it would be a bad thing to add a half gallon of purified water (boiled and cooled) into my beer during the bottling stage? I was thinking I could add it with the sugar in the bottling bucket before bottling. Is this a bad idea?

well i don't think you are risking oxidation anymore than you are if you boil 2 cups and add the sugar that way. it may give your beer a water downed taste. you can try it and see but don't expect it to come out right.