Always draft your own copyright page, save it on your computer and take a screenshot of the doc history to double make sure you make a time stamp before posting anything, after finishing chapter one. That was you have a legal record that can be used. It is cheap and even if you don’t finish the book it gives you a free insurance policy.
As for your writing—don’t let this sink your dreams or ambitions. You’ve made an incredible journey and first step. You will improve if you keep writing and pushing onward, and having a first book means you can contact an agent or promoter when the second one comes out. Stay strong and solid knowing you created something. History is full of thieves stealing from others.