Gauge can be confusing for everyone, so don’t feel alone! If you look on this site, you’ll see lots and lots of references to gauge questions!
'Nuf said. In your case, your swatch is too big. That means you need to go down in needle size at least one step, and possibly 2 sizes. Rework your swatch with needles that are 1 size smaller and see what happens. If the gauge is still too big, try it again with the next smaller size.
Now, that being said, here is a tip: When you are doing a swatch to test for gauge, don’t just work the number of stitches given. Instead, work at least 10-12 extra stitches. Then, when you go to measure for gauge, measure from the center of your work. This will give you a truer idea as to what your gauge really is. Also, when determining gauge, don’t get too hung up on the length. After all, you can always work a couple more rows to get the length!