When cutting the back blouse pattern on your fabric you have to do it two times.Once without the 2" extension and then with the 2" extension,since this is a blouse with the back opening. Also remember to flip the patten according to the right and left side.
When cutting the front blouse pattern you need to do it only once.Fold the fabric and place the front blouse pattern with the midside aligned with the fold of the fabric and cut along the pattern.To mark the darts I found that making slits through the pattern till the dart point ,allows me to insert the pencil to draw till the end point. Again flip the fabric and the pattern to the other side and draw the darts.Three in each side. The longer you make the blouse the longer the dart at the waist is going to be.