Sorry I'm late for class. I got tied up pretty good late in the day. But I'm glad the others picked up my slack.
Anyways, you may be able to just let the pipe sit on the vent opening. Some units, if it's the case, come with a 'clamp' or a screw to connect the pipe to the vent opening. At worst, if you think it's just not right, ctc. the Mfgr.