I am still studying ENGLISH English. is Would it be useful for me?
It is difficult to say whether or not the PET exam would be useful for you. What do you use English for? How long have you been learning? If your post #3 is an example of your best English, then you are not ready yet for this exam. You need to concentrate on capitalisation, punctuation and verb/modal usage.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.