Please check the option as mentioned by @sully, and If the problem is in detecting your fingerprints please delete your saved fingerprint.
There could be a problem in detecting the corners or tips of your finger. Add a new one and this time ensure that you scan all the corners and tips of your finger.
Follow the below steps:
Go to Settings >> Biometrics and Security >> Fingerprints >> Tap Add fingerprint >> Follow the instructions on the screen.
I hope it helps!