While glancing over my left shoulder and out the window as the bus struggled to reach the top of a narrow windy road
This is too much for the reader to interpret, and not enough imagery. Let detail is more. The mind of the reader get's this from the sentence: shoulder, window, bus, top... and that is it.
You need imagery and action:
While glancing out the window of the bus, I saw XXXXXXXXXXX. ---that is a sentence someone can interpret. You tried to start the essay by simultaneously telling the reader about your action and that of the bus. Limit the info in each sentence. Do not try to show to much in a single sentence, or the reader will see none of it.
Ha ha, I like this:
While glancing over my left shoulder and out the window as the bus struggled to reach the top of a narrow windy road, a bright green rain forest stretched as far as eyes could see, and still the ocean was nowhere in sight. ---I added a comma...I really like this as the first sentence. Look at how intriguing the start of the essay will be if you begin with this sentence. It's great. It shows one scene.
The bus dove back down the road and into the thick jungle canopy.----Awesome. This sentence makes that first part (which I crossed out, above) unnecessary, because it introduces the image of the bus.
Awesome, awesome... you write very well. As I continue to read, I don't want to suggest any changes; it's great. I hope I successfully shared with you the insight about not-too-much imagery all at once (i.e. that first sentence.) Show the reader one thing as you start an essay like this. :-)