Are you doing HSTs (HAlf Square Triangles)? There are different methods to do them. I'd suggest you find a tutorial or 2 and try those methods. One method, you sew them oversized and trim down to size aligning the 45degree line of you square ruler along the line where your colors meet. That is the way I do mine.
Here is an even easier method that Rhonda uses. All you need is a square ruler to accommodate your size.
http://www.quiltingboard.com/t-37915-1.htm