You've done everything right so far! Many instructors and designers choose to create their activities in Assignments before organizing the content into Modules, keeping in mind that modules act as containers for content delivery but don't in and of themselves constitute content. When I was building my courses, I created all the content first—not only the graded assignments, but also the discussions, pages, quizzes, and any other course content and activities—and only after completing that did I turn to module structure.
So now that you've created the assignments, you can add them to modules by following the instructions in How do I add course content as module items?
And if you'd like to learn more about the versatility of modules for course progression and organization, check out Share UDL Course Design Tips, Tricks, and Techniques
Good luck, Lucy! Stay safe, and stay well.