This story is first person from Ranma's point of view. This means that among other things, the grammar is less than perfect. Don't expect the Queen's English. Most grammatical errors as well as blatantly confusing shifts in verb tense are deliberate.
Most of this story is told in present tense. This does not mean that the story is taking place while it's being told. Rather, it means that Ranma is using a very casual narration style to relate the story of something that happened to him some time ago. Occasionally he'll switch to past tense. Don't let this throw you.
Because this is casual narration style, there are many clipped sentences, run-on sentances, and many apostrophes in places you would normally hear, but not see them.
These "mistakes" are here to add to your enjoyment of the story. They are meant to add color and to illustrate the character of the narrator. If this is something that is going to make the obsessive compulsive in you run screaming for the hills, consider not reading it. There is a lot of good fanfiction on the web, and lists of favorite stories are available on most author's pages. Please feel free to visit them. If, however, you would like to see this humble author's interpretation of the internal dialogue of her favorite anime character, please read on.