We all make mistakes with the squares. That's fine, as Sly said, it will just dissipate. It's only when you really mess up and get many word vibrations wrong, or the whole square for that day is missed that the square is broken - you start again.
This is not correct.
Unfortunately in this case explained by Winterwarrior666, they should start over.
The squares are fickle, this kind of mess up does dissipate the energies and make it worthless to continue the square.
If something like this happens what you need to do is detach completely from the energy raised on that days attempt so far, push it away from you and affirm the failed energy has no effect on the square you are doing and is completely detached from the square.
After that, take a break, preferably wait until the next planetary hour of the planet that day, or if this is impossible, wait for 10 minutes at least while voiding your thoughts and making sure all the energy from the previous failed attempt are gone and detached from the ongoing building energy of the square you are working on.
After that, restart the square for that day and be careful not to make a single mistake.
This method can work, I have successfully used it myself after learning of it from HP Zevios's sermon "Planetary squares FAQ".
However one must be careful with it and know what you are doing to properly detach from the energy while keeping the square intact and untouched.
Even this method is not guaranteed if one lacks experience or ability, but with practice it can be mastered and make doing the squares a lot easier as one doesn't have to restart the whole square when a small mistake is made.
Couching during the vibration counts as messing up the vibration, it messes up the energy of the square because the enumeration is interrupted when you re-do the same vibration.
Just 1 minuscule mistake like that is enough to trash your entire square, even if it is on the last day of a moon square.
You may still have benefitted from the energy, but the power of the square lies in its completion which crystallizes the energy in a permanent way that no other workings can really compare to, therefore when there is a small mistake this does not happen and the energy dissipates which is equivalent to a complete waste of ones work.
Using the above technique, you can reset the square for that day in case you made a mistake and redo it properly without messing up the square.
That said, if you have to use that technique a few days in a row because you make mistakes multiple days in a row, even if the technique is used properly, there is still a high chance the energy drops because there is too much interference.
One must be very careful and have a lazer like focus when doing the squares to prevent any mess up, which maximizes the energies raised from the squares.
HAIL ZEUS!