LingQ has a feature where you can submit your writing for correction from the other members. I am just starting to write sentences. You can see one I submitted for correction below. How long it takes to get a response entirely depends. These are not professional translators, but many are native speakers. For example, I am a native English speaker who will send feedback on sentences.
One advanced learner of English described the ‘Open Correction’ feature as so good that he doesn’t want to cure his addiction to it. In LingQ, you can make posts to their Forums, and then submit your posting for correction. In this way, making a habit of writing and getting corrections.
Talk to Me In Korean similarly has HaruKorean to get feedback from native speakers. My Korean pen pals also give me advice and corrections when I manage to put together some Korean sentences to them while chatting. Of course, KoreanDigitalAcademy class is a great way to get the teacher’s corrections. Maybe you have Korean friends you can talk to over dinner, greet the local Korean shop owner, or visit Meetups with other Korean speakers. I am sure there are many other ways to get feedback. Whatever way you do it, try to communicate and find a method for getting feedback.