Hi Alexis,
I have to say that I completely disagree with your teacher, and that your sentence is perfect! Well done!!
It is strong, yes, but from the voice of a passionate person who is trying to be persuasive, it is a very common and perfectly well formed phrase.
Where is your teacher from?
She probably wants you to substitute "must" with "should", by the way. However, for me, in persuasive speaking, "should" is too weak.
I hope this helps. Tom