Three quick questions to find out whether your trip is authorised, which OFAC category covers it, and what records you need to keep.
The Cuban Assets Control Regulations apply only to U.S. persons (U.S. citizens, U.S. permanent residents, anyone physically located in the U.S., and U.S. companies). If you hold a non-U.S. passport and are not ordinarily resident in the U.S., you face NO U.S. legal restrictions on Cuba travel. The only requirements are Cuban-side: a Tourist Card (Tarjeta del Turista, ~€25–30), travel-medical insurance valid in Cuba, and the D'Viajeros customs/health declaration filed within 72 h of arrival.