I did that.... You can't make those into 5x5. If we have to we would need 2.3 keywords.
here is an example
_ A D F G X
A a b c d e
D f g h j/i k
F l m n o p
G q r s t u
X v w x y z
So looking at this we can see that the letter pair AA=a AD=b AF=c and so on this is what I'm talking about.
So with your key word "portal" the encryption would look like this, XG GD FF AF GF GF DD GF GG XX FF FF FG FG FD FG FG FD GG FF FD GF AA FG XF DX FX DX GF XF GG FF FA -- -- AF.
Now with this 5x5 Polybius square it would be, NBNSDONNTGXWTLRSYJNJSOXNNXNRLEOXUS which is just random letters but don't count any words out yet, unless we have undeniable proof that we know the key word.
XG= y
You did t wrong
6x6: XG=0