In any case it is not easy to get D7 for GP. I am from NYJC and
I know most people there keep failing or borderline passing their
GP until the A levels, and when they take their A levels they do a
lot better. None of the people I know of have failed their GP. As
long as you are not a foreigner your English
should be decent enough to pass. Just predict what
questions will be asked (it's never hard to do that) and memorise
as many points as you can for those questions. Then during the exam
dump all the points into your paper. That should be enough to get
you at least a C5. In any case you will want to get a b4 for
english, cause the english module in uni (at least in NUS) can be
very time consuming.
Since you are still in J1 I highly recommend you to improve your
english while you can. Read more story books. Read newspaper. Even
reading New Paper can help your english.