redim preserve multidimensional array

I have two arrays........if an element is in both then dont transfer it to the "unique" array however, if it is in one and not the other then transfer it to the unique array. But for some reason the unique array is not increasing in size..........

ReDim unique_file_array(3, UBound(stdy_file_array1))
unique_file_array = stdy_file_array1


'For x = 1 To UBound(unique_file_array, 2)
'MsgBox (unique_file_array(1, x))
'MsgBox (unique_file_array(2, x))
'MsgBox (unique_file_array(3, x))
'Next x

MsgBox ("ubound unique is   " & UBound(unique_file_array, 2))

For x = 1 To UBound(stdy_file_array2, 2)
match_found = False
    For y = 1 To UBound(unique_file_array, 2)
        If stdy_file_array2(1, x) = unique_file_array(1, y) Then
            match_found = True
            Exit For
        End If
    Next y
    
    If Not match_found Then
    MsgBox ("in not match found")
        ReDim Preserve unique_file_array(3, (UBound(unique_file_array) + 1))
        unique_file_array(1, UBound(unique_file_array) + 1) = stdy_file_array2(1, x)
        unique_file_array(2, UBound(unique_file_array) + 1) = stdy_file_array2(2, x)
        unique_file_array(3, UBound(unique_file_array) + 1) = stdy_file_array2(3, x)
    End If
    

Next x

i found error.......when calculating ubound.......i used "Ubound(unique_file_array)" but it should have been "Ubound(unique_file_array,2)" to account for 2nd dimension.

see code below

ReDim unique_file_array(3, UBound(stdy_file_array1))
unique_file_array = stdy_file_array1


'For x = 1 To UBound(unique_file_array, 2)
'MsgBox (unique_file_array(1, x))
'MsgBox (unique_file_array(2, x))
'MsgBox (unique_file_array(3, x))
'Next x

MsgBox ("ubound unique is   " & UBound(unique_file_array, 2))

For x = 1 To UBound(stdy_file_array2, 2)
match_found = False
    For y = 1 To UBound(unique_file_array, 2)
        If stdy_file_array2(1, x) = unique_file_array(1, y) Then
            match_found = True
            Exit For
        End If
    Next y
    
    If Not match_found Then
    MsgBox ("in not match found")
        'ReDim Preserve unique_file_array(3, UBound(unique_file_array, 2))
        ReDim Preserve unique_file_array(3, (UBound(unique_file_array, 2) + 1))
        MsgBox ("ubound unique is   " & UBound(unique_file_array, 2))
        
        unique_file_array(1, UBound(unique_file_array, 2)) = stdy_file_array2(1, x)
        unique_file_array(2, UBound(unique_file_array, 2)) = stdy_file_array2(2, x)
        unique_file_array(3, UBound(unique_file_array, 2)) = stdy_file_array2(3, x)
    End If
    

Next x