Hi Grace,
Im sorry to say this and this comment will not solve your problem, but just to add something, Vegas Pro is good for editing such like cutting/adding/moving clip but when comes to render.. its too much of trouble, some pro user/editor do use Vegas pro to cutting clip but yet export their project to premiere pro or other software which has nothing to worry about final result error.
many will disagree with my comment but only some knows the real pain getting bad end result after so much of hard work editing, color grading and more but yet the end is bad.. Im not telling vegas pro is totally bad, its makes our editing much faster than other software but for kind of heavy/long/bigger project its not reliable. worst if working and rendering on 32bit floating point (full range).. yet I totally agree with those pro editor that use only vegas for cutting and arranging clip.
Thanks..