Texas Instruments Ti-84 plus Graphing calculator - Black

Is this an authentic one? I bought this calculator as it’s critical to my math course in school, assuming it would work considering the price. But every time I type in an equation or try to plot a graph I get error, when my classmates and teacher are doing the same exact steps and theirs are working just fine. Mines also brand new, I didn’t buy a second hand one so it’s not like there would be a problem with the settings.