yes, those are the correct dimensions. As Tellabella mentioned, trimming is the all important step. You want the point of the triangle to be 1/4" from the edge and the seams on the other side to run right thru the point of the rectangle. If you sew with the correct seam allowance, your block will go together well. If you haven't verified your seam allowance, you might want to check it. Here's a good method:
http://www.quiltingboard.com/tutoria...ce-t89997.html
remember, you don't really measure the seam, you measure the resultant patch.