Yes, this is the way the law, prosecution and judgement works. If you violate GDPR and the EU prosecutes you and you don't even show up to court and there is judgement against you and you are fined, the EU can try to get paid from your bank. That's how law, prosecution and judgement work in America too. How else would it work? Why would anyone obey any regulation or ever show up to court otherwise?

That being said, the starting point shouldn't be, "there's no need to imagine that I'm violating GDPR. I only serve Americans". The starting point should be, "I had better imagine that I might be violating GDPR even though I only intend to serve Americans. Are there things I haven't considered? Are there resources I should seek out? As a service provider of some kind, hadn't I better spend a day or two imagining the ways I might run into trouble and plan to avoid it?"