How JK flip flop works?
You are not done yet.

After Q changes to 1 at step 5 you need to go back to revisit step 2.
Q' now becomes 0. This feeds back to G1 and keeps Q at 1.

There are not necessarily just \$n\$ and \$n+1\$ values of the signals. You need to keep propagating the changes through the circuit until no more gate outputs change state. At that point the circuit is stable.