Yes it is possible to join two pieces together, whatever the shape. Of course, there are different techniques of joining. With this being crochet, I generally use the whip stitch, but there's also a certain way to join the pieces so that it matches.
Do you have a link to the pattern so we can help determine what join would be appropriate?
And here are some links to help you along:
(about half way down "Joining Seams")
I've tried looking for some videos to help you along but no such luck. :(