It’s a good idea to get your own blog on your own domain. And then cross post on all other platforms. But it’s too much of a hassle if you’re a beginner.
There are various platforms to get started with blogging like. My preference would be in this order:
So what you can do instead is: post it on any of the platforms mentioned above, wait for 2-4 days, and then cross post it on other platforms as well. Use your social media handles to publicize it. Check this article on cross posting if you’re serious about blogging. For this competition however, you don’t need to do so much. Just get few blogs published.