Help with a pattern? Where to increase

I really hope this is in the right section… I browse this forum occasionally but I needed help so I made an account just for this!

Cast on 21 sts and work in garter st back and forth, AT THE SAME TIME inc 1 st (work 2 sts in 1 st) in each side every other row a total of 22 times = 65 sts.

That’s what the pattern says. Where do I do the one increase in each row? Does it matter? I’m thinking I’d just do it at the beginning of each row because then it would alternate sides… but I don’t know.

Thank you!

Here’s a link to the pattern, if needed:

I couldn’t put it in the original post because it was my first, and apparently you can’t put links or images in your first post.

Each side means each edge, so you would increase at the beginning and end of every other row.