help? I deleted images from my Memory card, but my camera still says Memory Card full?

[Guess Who]

Hi, I am new to photography, and I have a Canon Rebel XS. I brought a brand new memory card sd, so i wanted to delete all the photos from my camera, so i slid the memory card into my mac computer, where I deleted images from the ds card. After I put the card back into my camera, i can not take pictures, because it says that the memory card is full, and I know the memory card isn't locked either, So please tell me, what do i do??