Is there any way I can turn off FireVault while it is encrypting my data?

Unfortunately you need to let the process continue. Make sure to keep the laptop booted and plugged into power so it will continue the process when you are not using it. If the laptop has a hard drive this can take a lot of time even if the drive is healthy. Some users on here report the encryption/decryption process can take days or even a week.

Are you using a hard drive? Perhaps the drive is failing or you could have a bad hard drive cable. You can check the health of the drive using DriveDX. If DriveDX reports the drive as healthy or you are using an SSD, then post the DriveDX report here using the "Additional Text" icon which looks like a piece of paper.

You could also try running the Apple Diagnostics or Apple Hardware Test depending on the age of the laptop, but DriveDX will provide more reliable results and information.

Just to amplify what HWTech has already said:

Changing the setting for FileVault taks only a moment. But converting your drive from one way to the other requires that each and every block be read in, changed, and written out.

The conversion will remain in process, and your Mac will be slow, until it has been able to change the entire drive.

Running with an encrypted drive takes no longer than an un-encrypted drive. There are machine instructions that do most of the encryption/decryption on the fly, really fast.

You MUST have a trusted Backup. If an encrypted Boot drive dies, everything will likely be lost.