Yes I planted it slightly below ground level initially which l hope I can work around with some of the input here (thanks for all the help so far!)?
I carefully removed most of the topsoil this afternoon but then it started raining. Hopefully not too much rain water is trapped on top. Initially, I planted the tree on a slight decline, with the thinking that water will naturally roll down the slant and into the lake water about 10 - 15 feet behind it, instead of having the tree sitting in a pool of water. I hope that theory helps right now haha!
After calling around,I'm making the trip to the Bushel Shop tomorrow and picking up the mulch. Lots of places don't have unmixed Cypress Mulch. The nearest one I found will take me the same time as driving to Bushel Shop (excluding Lowes, HD etc).
So once I have the mulch, I'll dig an additional 2-3 feet around the plant, remove as much of the topsoil as I can (being careful not remove much of the soil the plant was potted with), and fill that with the mulch. This still won't fix the depth issue though. Should I do anything about that?
Thanks again for everyone's help!
EDIT: Just ran outside quickly to check the mango plant, and nope, no pool of water resting on my mango plant!