It asked for a 10 gauge, I think I have 8.

It says 66 stitches, how do I make up for that? How many stitches?

It’s easier to go down a needle size to get gauge if gauge is important. If you’re making something like a scarf, it’s not as critical. You can increase the number of stitches for a pattern repeat, or if there isn’t a pattern, increase until it’s the size you want.

Here’s a good article about swatching and gauge: