Hi saulzar,
You might have secured very good grades at high school, however you cannot compare GMAT with the other high school exams. GMAT is not only test of your content knowledge but also test of your time and stress management skills. Moreover, GMAT English is slightly different than any other exam.
Your teacher did guide you correctly to take the GMAT Prep, so that you know your level / your baseline score; and hence, you can plan accordingly to achieve your target score.
Looking at your score, I would suggest get your basics clarified and much more importantly look out certain necessary tips and strategies, which works best for you, and try to implement as you progress in your studies.
You do have good set of study material. Also, try to practice OG questionnaires (OG13, Verbal/Quant Rev, etc.)as these are almost replication of actual GMAT questions.
2.5 months is a sufficient amount of time to complete a prep course.
Finally, keep your self-confidence and zest always high, and do not get disheartened due to such minor hick-ups; these are just to open your eyes and make a perfect path forward.

All The Best!!
Hope this helps..

Thank you for the kind words.
I forgot to mention i have the OG12 + verbal/quant guides as well.
The test somewhat made me even more determined. Im gonna beat the GMAT no matter what.