score:6
Don't worry a bit. Message them to say that you will need to do some more changes and they will unfreeze the application so you can make further changes. Just repeat it if you make any mistakes.
If by any god known reason, they cannot unfreeze the application, don't worry a bit. Go to the TLS contact centre and when you enter ask them that you need to do some changes. They will provide you with a new printed form, which you can fill it there. They may crib a bit, but don't worry. People are quite lenient at the centre. I have seen many Chinese students fill up their form again at the contact centre.
Else take a printout of the application form and fill it by hand, before going to the processing centre.
A caveat though, I am talking about London. I am not sure about other places, but I wouldn't assume the processing centres would be filled with idiots who wouldn't allow you to fill in a new form.