"I'm fine on my own"
Some readers will have bristled at the last chapter. You like your own company. You find people tiring. A weekend with no plans is your idea of a good weekend. You've no wish to be told you're secretly lonely, or to be pushed into a busier life than you want.
I agree with you, and I'll say so without any hedging. Solitude that you choose is one of the good things in life. Some people need a great deal of it, and they're not broken. If you see as much of other people as you'd like, feel no pang about the ones you don't see, and would call your life full, then you don't have the habit this book is about. Nothing in it applies to you, and you can stop reading with a clear conscience.
The distinction that matters is the one Cacioppo and Hawkley draw. Being alone is a fact about your diary. Loneliness is a gap between the contact you have and the contact you want. A person who wants little and has little is content. A person who wants a moderate amount and has little is lonely, however self-sufficient they look. How many evenings you spend by yourself doesn't settle which you are. What settles it is whether something in you would like it to be otherwise.
I'd suggest an honest check in place of a label. When you passed the name in the list, was there a pang? When a friend does ring, and you talk for forty minutes, do you put the phone down feeling better than when you picked it up? When a plan you'd half dreaded turns out to be a good evening, do you think afterwards that you should do that more often? If so, you want more contact than you're getting, whatever your temperament.
The label "introvert" can work against people here. It describes something real. Some people do find company more draining than others, and need more time alone to recover. But needing time to recover from company is quite different from not needing company. Most people who call themselves introverts have a few people they love to see, in small numbers, in quiet places, for a limited time. That's a preference about quantity and setting. It doesn't mean preferring nothing. If the wait has reduced your contact to below even that modest level, then your temperament isn't being respected. The label is being used to explain a shortfall.
Epley and Schroeder's commuters, from chapter 4, are relevant here. People predicted they'd enjoy the journey more in solitude. When they talked to someone, they enjoyed it more than those who kept to themselves. The summary I read doesn't say whether this held for the quieter participants in particular, so I won't claim that it did. But the general point stands. Our forecasts about how much we'll enjoy company tend to run low. "I'd rather stay in" is a forecast. It's sometimes right. It's wrong often enough to be worth testing.
If you're on the quieter side, what I'd take from this is that the first moves you make can be shaped to suit you. You needn't throw a party. You can ring one person. You can suggest a walk, which is side by side and has a natural end. You can see people for ninety minutes and go home. The rule in chapter 13 says nothing about how much company to have. It says that when you think of someone, you tell them. A person who does that and then sees one friend a fortnight, on terms they find comfortable, isn't lonely. A person with the same temperament who does nothing may well be.
So you may be right that you're fine on your own, and you're the only one who can know. Answer it by the pang, though. The label can't tell you.