Customizing a Patterns cast ons

I want to make this afghan pattern a little wider than the pattern suggest. It calls for 96 cast ons. Since one row is K1 YO and K2to to end and another row is P1 YO P2to to end do I increase my cast ons by groups of four or three? (96 CO + 3 stitches to increase afghan width)

By 3. Does it have edge sts?

Thanks Suzeeq. Not really, But it ends in a K or P.