When working with a new pattern, it's always a good idea to make a test first in inexpensive fabric.  All you need are the basic front, back and sleeves basted together to check for fit in shoulders, length and room.  Muslin is fine, or look for clearance fabric.  If you can't do this step, then at least try to cut generous seam allowances and baste pieces together before sewing final seams.  Try on and adjust where necessary.