use the Electra Jailbreak Remover Toolkit by
@pwned4ever for iOS 11.2 – 11.3.1 to remove my jailbreak on iPhone on iOS 11.3.1! You can get it now here
you don’t need to lose your data.
It’s already made into an ipa for everyone, if you install the vfs one with cydia impactor and you might be able to use extender to resign.