Knitting a border?

i made an afghan that is in all stockinette stitch, and from the very beginning i have been planning on adding a garter stitch border to the outside. in making a tiny version of it, i did the border perfectly, by looking off a website, but when i try and do it now it wont work.

does anyone know how to knit a border so that it looks good and/or clean?

Which pattern is it?

I would figure how wide I want the border to be and then allocate enough stitches. The afghans I have knitted have been mostly 3 stitches wide. You would knit the first three rows of the afghan and then go to K3, stockinette across and finish row with K3. Always knit first 3 and last 3 stitches and alternate K and P on body. To finish K last 3 rows of afghan.

Adding the knitted border after the fact can be done a number of diff ways. How large is the afghan? Are you planning to work each side separately or attempting to do all four sides at once on a very long circ? Do you want to work mitered corners? Did you work selvage edges of are all in st st?

You might also consider crocheting the border. Doesn’t req putting large number of sts on a ndl and you can rip back more easily if you want to change the look.

(Attached is crochet border on afghan that was worked in all st st.)