Welcome to the Community, Heather. Sounds like you are making excellent progress.
As others have said, C will come in time. Have you tried the exercise where you fret the chord, lift your fingers just off the strings but still keeping the shape, and then fret the chord again. Progressively lift the fingers further from the guitar as you progress until you fret the chord, touch your knee, fret the chord.
To keep engaged in consolidation, I suggest recording yourself playing songs. Pick songs as suggested by Justin, choosing a song for each step taken in the Grade ie start with eg Born in the USA which uses A and D, then one with A D E etc. You can record yourself playing along with the app. A few people have posted recordings with the App inserted in the video which was fun.
Then share those recordings in AVOYP, you can post the first few here. In my experience sharing recordings was one of the best things I did when I started up with Justin’s Lessons. You’ll get feedback and tips, loads of encouragement, and feel-good on your progress.
Enjoy the adventure!