[xiamenese]

Did you create the central shape first, and since you have the two outer shapes with a bottom border and a right border for the right hand one, is the central shape actually the size of the whole diagram? Do you need it to be so? Do you want the border right round the whole object or only round the central part?
Are you using OG or OGPro? If the latter, can you produce the three shapes without border independently and then 'union' them and put a border round the resulting shape? I don't know ... I'm just guessing and that's what I'd try.