mass/volume

I learned that matter has a mass, volume, and takes up space. Also i did a chemisrty lab: Measurement in Chemistry where i had to predict the mass of certian items such as, a penny, a nickel, a marble, a black rubber stopper, a green rubber stopper, a container of water, and a fishing weight. After predicting the mass my group actually measured the item on a pan balance. My predictions were pretty off compared to the actual mass of the object. i guess i need to work on making good predictions. Also in the same lab i had to guess the volume of certain containers such as a small test tube, a small glass bottle, a paper Dixie cup, and a plastic cup. after making my predictions my group had to fill the container with water and pour it into a 100mL graduated cylinder. My predictions were also off again, according to my calculations. I never predicted the right amount of mass or volume for any of the objects. :(