First of all, the figure above is a trapezoid, not a rhombus. Second, you cannot make it into a triangle because then you wouldn't be able to make it stand.
Place the melted chocolate in a Ziploc baggie or piping bag, then pipe two vertical lines that are parallel to each other, then two horizontal lines on top of those....
Chances are, your lines are set to spiral towards the center. On the computer version, open the settings and click on "Spiral towards center" to turn it off; on iOS,...