My sister recommended I add my T2202, however when I did so it halved my return, she told me it is not supposed to do that, what is wrong?

What likely happened is that you put in employment income, so TurboTax claimed the Canada Workers Benefit (CWB) (aka the Working Income Tax Benefit) for you. This is a refundable tax credit for people who work, but don’t make very much. However, students are usually not eligible for this credit, so when you added your tuition, then the CWB was removed, lowering your refund.