I am afraid I cannot comment over the content in its entirety since I read couple of initial paragraphs only. As to the language part, I reckon that you know tenses good enough and have a decent cache of impressive colloquial words (which sound neither complex nor archaic). Here are few suggestions that may come in handy:

1. You should work on your punctiation, esp the use of semi-colon

2. Writing long sentences in a timed exam is a recipe for disaster. Long sentences entail exceptionally good punctuation and if you find punctuation dreadful, AVOID using long sentences. Unless it is an academic write up (like a research paper), long sentences have the propensity to annoy many out there.

3. Focus on the rules pertaining to correction of errors. These rules tell you about those subtle technicalities that are compelling, yet often go unnotoced.(e.g where you use "in" and where you have to use "into").

Godspeed!