Have you looked at the angles in the triangles drawn? It might help to draw in some radii and work out angles from the centre.
How will you record the triangles you can make? You might like to print off these sheets if you're not using the interactivity:
Sheet of
three-peg boards
Sheet of
four-peg boards
Sheet of
five-peg boards
Sheet of
six-peg boards
Sheet of
seven-peg boards
Sheet of
eight-peg boards
Sheet of
nine-peg boards