Copywriting requires a different skill set. It requires one to understand marketing and to present a service or product in a way that leaves people aching to have it. It generally requires copy that is concise and formatted in a way that is much different way then other writing forms. It involves understanding human psychology and doing research so you understand what your target audience wants and what they will respond to. It is precise and needs to grab attention right away. It involves setting aside what you want, as the person selling the product or service, and instead requires that you get in the head of your target market and speak directly to their wants and needs.
Be sure that you are thinking like a copywriter when you are writing your marketing copy. Otherwise your writing will not be effective, no matter how good of a writer you are. Happy copywriting!