If I understand you correctly, You are making a solid from 6 octagons and 6 equilateral triangles, with all sides/edges equal to 1 inch? In that way, each octagon should be less than 2.5 inches wide and 2.5 inches tall.
[To prove: take a 2.5 inch square, measure a fourth of the way (.625 inches) on both sides from each corner/vertex and mark. Draw a line connecting each pair of marks at each corner. Slice off all 4 corners along the line to form 8 new corners of 45 degrees each.The sides/edges should all be a bit more than 1 inch each.]
Make sure you are measuring correctly. The triangles are 1 inch wide at the base and, because they are equilateral (60 degree), less than an inch high. You should be able to close-pack the octagons (2-1-2-1 staggered array)with plenty of room for the triangles, if I'm not mistaken. I'm assuming you aren't adding tabs, but even then, it should fit, unless my geometry has gone horribly, horribly wrong! Disclaimer: I am not a Math major or a mathematician of any kind, but I do like origami and papercrafts! Good Luck!
