Remember that it’s okay not to want to send naked photographs of yourself, as there’s always the risk they may spread to other people.
Once you’ve pressed the send button, those photos are completely out of your control, and the receiver could do anything they want with them.
The best thing to do, especially if you’re uncomfortable with the request, is to speak to your significant other. Explain to them you just aren’t comfortable, and you’d never send naked photos to anyone. If they care enough about you and your feelings, they’ll understand where you’re coming from and forget the conversation.