Hi cynthiafromcave creek,
Your Mac doesn't have the T2 Security Chip or the Apple M1 chip. Because of this, your Mac doesn't have hardware encryption capabilities.
When you turned on FileVault, your Mac generated a recovery key, then started to encrypt your internal drive. Because you don't have hardware encryption, your Mac has to manually encrypt your entire drive, which will take a considerable amount of time - especially if you have a large internal drive. (Keep in mind, your Mac isn't just encrypting the used space on your drive, it's encrypting the ENTIRE drive - including free space.)
To ensure that the encryption process continues to complete, keep your Mac plugged in as much as possible. Encryption will automatically pause when your Mac is on battery power.
Once your internal drive is fully encrypted, you should be able to turn off FileVault without any issues. Of course, that will start the decryption process, which will take an equally long amount of time to complete.
To view the encryption/decryption progress (assuming that you're running macOS Catalina), open Terminal and run the following command:
diskutil apfs list