If you just turned it on, you can use the following instructions from Two-factor authentication for Apple ID - Apple Support
to turn it off:
If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll for two weeks. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require higher security.
Also note that the code should be sent to all of your devices -- including the originating device; i.e., you don't need to have a second device with you. The two factors are not two devices, they are your password and the code. I use two factor with one device all of the time (although I would also recommend having multiple trusted phone numbers which can be Android and landlines).
