You have already proven that
• You can write to a specific word length.
• You can deliver the article on the deadline.
• You can handle rewriting the article if requested.
• You're committed to writing and you want to grow.
Like many professionals, I started with articles and wrote my first one 18 times before I sent it out. Fourteen of those times the piece went through my editing group, the Scribe Tribe. Within a month after sending the first article, I received a check. As I continued to write, sell articles, and received a few rejections, I also began to understand how publishing works.
It still amazes me that want-to-be-successful writers get an idea for a book, write the entire manuscript, and haven’t learned the craft. Often they don't even know what professionally written manuscripts look like.
Writers want editors to consider them professionals. Professional writers prove their commitment by their knowledge of the craft.