Making buttonholes

I’m a novice knitter and this is my first question I’ve posted on this forum. I’m knitting a baby sweater and am at the point of making the front border and button holes. When I follow the pattern the buttonhole is waaay too small. Maybe I’m doing it wrong or else maybe I need to change the pattern to make the buttonhole larger. This is how the pattern reads:
Next row: Rib 4, cast off 1 st, (rib 15, cast off 1 st) 4 times, rib 3
Next row: Rib 4, cast on 1 st, (rib 16, cast on 1 st) 4 times, rib 4
If I need to increase the cast off and cast on how would the new pattern read? Also what stitch do I use to cast on for the second row.
I appreciate any help anyone can offer!

Next row: Rib 3, cast off 2 st, (rib 14, cast off 2 st) 4 times, rib 3
On the next row, cast on 2sts when you come to the cast off sts.
You could do a backwards loop cast on but I think a knitted or a cable cast on gives you a neater cast on for buttonholes. There are videos for both on the Free Videos tab under Cast Ons.

Thanks so much for the help!