Are you using a pattern? If so, can you post a link to it?
If not, how did you make the bottom? Did you just make a rectangle? If so, all you'd need to do is follow the instructions on the video located in the Basic Techniques section. Mouse over & click on "...more", then scroll down to "Picking Up Stitches aka "Picking up stitches and knitting".
OTN: Merino Stripes Curved V-Neck Vest, Counterpane Preemie Blankie (3 squares done!), Baby Bunting in Brioche Stitch, 2 Twice-Knit Snuggles, 3-D Honeycomb Snuggle, Cat Sweater, Preemie Beenie
Recently Finished Projects: 2 felted mobius cat baskets, MANY Lace Washcloths, The Magic Scarf from HELL, 6 Knitted Lace XMas Balls in crochet thread, Lace XMas Ball in mohair, 4 Initialed Washcloths, 2 Lacy Soap Socks (1 knit, 1 crochet), 2 Seamless Rectangle Snuggles (one outside in, one inside out), XMas Tree Illusion Snuggle, 3 scarves for presents, Fisherman Knit Snuggle, Turkish Stitch String Bag, Wheelie Steering Wheel Cover, Moebius Cat Basket, 9 Snuggles, Preemie Hats, Sandy's (Felted) Cat Basket