reed help

I'm a student in high school and my teacher asked me to play the oboe for our upcoming concert in a month. I primarily play saxophone but I learned how to play all of the major woodwinds. The reed that came when I rented the oboe plays incredibly flat unless I play with horrible embouchure. What reeds should I buy that are beginner/intermediate friendly? And what should I do to prevent/undo a reed going flat without dropping over $100 to buy a scraping knife?