I Am A First Time Breeder Of My Boston Terrier. We Are Not Quite Sure If She Is Pregnant But She Is Leaking Stringy Gooey Stuff From Her Vagina? What Is Wrong?

Leaking of gooey like discharge from the vagina of dog is not the sign of pregnancy but it can be sign of delivery. If she is with full term then there bare chances that she is about to deliver. If she is pregnant and the delivery is not due in near future then she can suffer miscarriage. As you are not sure of her pregnancy, she might be suffering from any infection. It will be good to take her to Vit diagnosis and treatment.

Discharge like you are describing is not diagnostic of pregnancy.  Gestation (pregnancy) in dogs lasts 63-66 days.  So if she was bred a little over 2 months ago she may be starting her labor.  Uterine enlargement can be palpated at day 26-20 of pregnancy.  Pregnancy can be diagnosed on ultrasound as early as 20-22 days but more reliably a few days later.  The fetal skeletons calcify at day 45 and can be seen on x-rays.  Pending when your dog was bred your veterinarian may want to run an ultrasound or take an x-ray.
In the first stage of labor they can pass a mucous plug from the vulva followed by the start of labor. 
 A uterine infection (pyometra) can produce smelly, thick (gooey), pus-filled vaginal discharge.  Pyometra is usually noted in the month after heat but can occur at any time.  This is a serious and potentially life threatening problem.
She needs to be seen by a veterinarian to determine if this is infection, if your dog is pregnant, or what type of discharge is present.  They will take a swab of the discharge and examine it under the microscope and take x-rays.