Key thing to think about:
- the rhyme scheme as ABCBBB means that "B" lines will all rhyme with the last word
- I think "16 15 16 15 7" is talking about syllable count, so we need to make sure our first line has 16 syllables, etc
      I am afraid of the water, as it can be scary down deep
      With the unknown terrors lurking beneath the murky, dark blue
      The things we do not know under the surface cause me great dread
      For unless I find out, these unknown frights will be ringing true 
      Because I cannot see through
      These great fears of the depths are mighty, and will never go askew
      Thinking about the extensive sea can make me queasy
      The thoughts swirling of it swallowing you up with jaws of darkness
      Your lungs fill quickly with water, unable to breath easy
      Leaves me hugely uneasy
                  (I am not actually afraid of water lol, but there are a lot of words you can use haha! I hope this will work for your assignment!)
Have a nice day!
     I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather