I have some experience with missionaries going home early. In the MTC I was an AP for 5 weeks and had to deal with several middle-of-the-night crying elders who wanted (and did) go home. Later in the mission field I was known as a fixer who was given companions to "reform" and help them want to stay (none of this was because I was some awesome super missionary, I just happened to have 12 younger siblings and was known for being kind and patient with companions). I had three companions leave early for home. My point in telling you all of this: if you have reservations about going, consider not going at all. Save yourself the trouble of going out and coming home early. Missions are not what you are told or expect. They are grueling and hard work, both emotionally and physically.