Hmmmm . . . I'm not sure what you could do differently. I really like that bed though. My dogs love those little round beds. I'll have to check when I get home, but I think that theirs are stuffed fuller around the edge and the bottom is possible sheets of poly. I'm not really sure.
Would you be willing to share how you made it? I can always use another dog bed and If I could make them it would be even better.