May I sell something I create on Sundays, for relaxation?

Six days a week I do my duty with the daily grind. On Sundays, I go to Mass, and try to keep the Sabbath holy, and relax.
The trouble is, my idea of perfect relaxation is to write stories. These are wholesome family oriented stories with a good message. I feel very compelled to create.
But if I do this on Sundays, may I not offer them for sale? I have always wanted to earn my living by using these gifts, though the chances of getting published are admittedly small. But I want to try. There is no other time to write other than Sundays. I typically have some hours on my own as my family live very far away…and I enjoy writing so much.
My concern is that if I write on Sundays, I may not offer this work for sale, ever.

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