You've got a few clear options.
My suggestion for best option:
1-Keep the 5 gal carboy for secondary & special stuff, you'll use it for sure!
2-I'm fairly positive you're talking about Brewing Classic Styles which iirc, I don't own it but have read, they tell you how to easily convert the recipes to 5 or 5.5 gal recipes. Find it and follow it.
3-Buy 1 or more 6.5 gallon standard size beer fermentation buckets.
Brew 5-5.5 gallon batches.
4-Most important of all is the one recipe book you have isn't a bible, period. Being semi-new and brand new to 5 gal. brewing I'd simply buy 5 gallon recipe kits from either the LHBS or one of many fine online outlets. Buying kits is a great route because you can supplement recipes easily. Say you read about what Special Roast adds to brown ales & stouts. Order a kit in that style and an extra lb of Sp. Roast, then add 1/2-3/4 lb to your steeping grains/mash. Voila, you've experimented, added character, found new information and are a better brewer!
5-If there aren't instructions in the book to convert your recipes use Brewer's Friend or Brew Toad websites to enter your ingredients for 6 gal batches with perameters set to 6 gallons then reduce the size to 5 gals and have the site convert the quantities down for you. The general rule for most recipes is going to be, keep everything the same but reduce the base grain or malt extract amount by 17% (the difference between 5 & 6 gallons).
6-READ, spend time reading not just online forums but any homebrew book you can find. Brewers Publications puts out lots of quality material. BYO & Zymurgy magazines along with a few others are excellent sources.
Other options include fretting, measuring tiny amounts of hops, lots of math, frustration, and even ignorance about the subject matter. Nothing wrong with ignorance, all of us are ignorant about more things than we're educated about. However if I want to increase the off-road performance of my jeep or consistently brew good beer I'm gonna educate myself on the subject, choose a path, and pursue something close to perfection within the parameters of the target. Not busting your balls at all, you're actually seeking information, but driving home the importance of familiarity then you'll be comfortable enough to choose a direction and pursue it!
Best of luck! Hope at least some of what I suggested helps, Schlante!