Sounds like you're doing fine. You don't have to be a member of GWA but we would welcome you and if you do join please name someone as your sponsor as it would benefit them. Before I submit anything to anyone I have my wife proofread it as she is very good at catching my mistakes.
I suggest you have someone fairly competent read over your material before you submit it. I think that would only serve to make you look better in the eyes of the editor.. Usually magazines will have writer's guidelines and they will tell you how soon you can expect a reply. If you don't have a reply within their time frame then give them a call. I hope others here agree with my suggestions

These are a few things I've learned about gardening AND writing:
1. You never know if the seeds youÂve sown will growÂsometimes the things that look promising wither, while other plants flourish against all odds. Therefore, never assume that something will do well and plant large amounts of everything.

2. Sometimes things take longer to grow and mature then you expect.

3. The garden is never finishedÂthe work is always in process, and the process itself is rewarding.

4. One year you have a bumper crop and the next year nothing; one plant is spectacular and other things sulk. See number 1.

5. All the good stuff (gardens, meals, work and love) are better when shared. Yes  join GWA.