Are you referring to the flag used by the Confederate States of America or the Confederate Battle flag?
Many people, commonly, confuse the two!
Below is a bit of history, for you to share with your teacher and class.
I'm sure you can find some pictures of these flags, which will help you and others to understand the diffferences in the designs.
There were 3 official Confederate flags.
The "First National", aka "Stars and Bars", adopted by the Provisional Congress, 4 March 1861.
The "Second National", aka "The Stainless Banner", adopted 1
May 1863 to 4 March 1865.
The "Third National", last flag to be officially adopted by the Confederate Congress, on 4 March 1865.
The "Confederate Battle Flag" (red background with 13 white stars on the blue X) was the flag used by the Confederate Army, and was submitted to the Confederate Congress on 4 March 1861, by Mr. William Porcher Miles.
This flag was used on the battlefield, in order to identify and track troop movements.
Unfortunately, this is the flag which has been bastardized, by a minority of uneducated people whose only desire is to promote hatred, racism and intolerance.