The obligation laid down in paragraph 1 of this Article shall not apply to:
* processing which is occasional, does not include, on a large scale, processing of special categories of data as referred to in Article 9(1) or processing of personal data relating to criminal convictions and offences referred to in Article 10, and is unlikely to result in a risk to the rights and freedoms of natural persons, taking into account the nature, context, scope and purposes of the processing; or
* a public authority or body.
But that doesn't matter to you. As long as you're too small to have a server and a (part-time) "controller" inside the EU, you seem to be out of luck (note: IANAL; there might be another way; cooperation with another small company, perhaps?).
https://gdpr.eu/compliance-checklist-us-companies/