Question about video recording and size of the recording on a tv/comp

So i just started editing my iphone movies with imovie for mac. However I ran into a problem right away. When i recorded a video while holding my iphone vertically the playback was horrible on my mac because it was so skinny and not wide at all. First off I was wondering if there was a some way to make it wider? My videos that were recorded while my iphone was horizontal then they are perfect when viewing on my mac. So if anyone can help me with this question i would greatly appreciate it.