To start with when you make a tortola or tobago out of knit you will NOT cut on the bias and you WILL use woven facing.
To get the triangle hemline you will redraw your pattern piece as shown by the red lines below - do this for the front and back pieces. You do not need to do the dart since it is knit and loosened on the fit. Then simply sew as per the directions!
The back view:
Simple, flowy, and comfy for summer!
EDITED: Someone asked in the LAB how to get the more down the sides handkerchief hemline look so I thought I'd let you know how here too: