BottomSheetDialogFragment opens half

By BottomSheetFragment you mean BottomSheetDialogFragment . To open expended sheet you need to make some changes in onCreateDialog().

 @Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    BottomSheetDialog bottomSheetDialog=(BottomSheetDialog)super.onCreateDialog(savedInstanceState);
    bottomSheetDialog.setOnShowListener(new DialogInterface.OnShowListener() {
        @Override
        public void onShow(DialogInterface dialog) {
            BottomSheetDialog dialog = (BottomSheetDialog) dialog;
            FrameLayout bottomSheet =  dialog .findViewById(android.support.design.R.id.design_bottom_sheet);
            BottomSheetBehavior.from(bottomSheet).setState(BottomSheetBehavior.STATE_EXPANDED);
            BottomSheetBehavior.from(bottomSheet).setSkipCollapsed(true);
            BottomSheetBehavior.from(bottomSheet).setHideable(true);
        }
    });
    return bottomSheetDialog;
}

Just keep the layout match_parent no need to use NestedScrollView. It worked for me . Let me know if you still face problem .

In case someone is using New Material library . Which is
implementation 'com.google.android.material:material:1.0.0'. Then you need change the id of Parent FrameLayout. So it will be .

 @Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    BottomSheetDialog bottomSheetDialog=(BottomSheetDialog)super.onCreateDialog(savedInstanceState);
    bottomSheetDialog.setOnShowListener(new DialogInterface.OnShowListener() {
        @Override
        public void onShow(DialogInterface dia) {
            BottomSheetDialog dialog = (BottomSheetDialog) dia;
            FrameLayout bottomSheet =  dialog .findViewById(com.google.android.material.R.id.design_bottom_sheet);
            BottomSheetBehavior.from(bottomSheet).setState(BottomSheetBehavior.STATE_EXPANDED);
            BottomSheetBehavior.from(bottomSheet).setSkipCollapsed(true);
            BottomSheetBehavior.from(bottomSheet).setHideable(true);
        }
    });
    return bottomSheetDialog;
}

Make sure all your imports from import com.google.android.materialin this case.