Very simply put, you can be fined $7500 for just going to Cuba, regardless of the reason. It is pretty much illegal to travel to Cuba…from the US side, not the Cuban side.
Cuba will welcome you and stamp only your visa if you ask them to and not stamp your passport so when you return to the US, your passport will not say you have been in Cuba.
So, when you return from Cuba, US customs very well may ask you if you have been to Cuba. You then make the decision to lie or face the penalities.
Search for OFAC for more information. Good luck.