My contact perscription from eye doctor was a -2.00 in both eyes. is that strong? when is someone considered legally blind?

No: -2.00 would be considered a low amount of nearsightedness. Legal blindness does not have anything to do with the magnitude of your prescription. It has to do with how good your vision is while wearing your correction. Definitions vary by state but generally vision of 20/200 or worse with the better seeing eye is the criteria. At -2.00 your vision would be better than that even without correction.

Refraction: Minus two myopia is a mild degree of myopia. Legal blindness is usually defined by visual acuity being worse than or equal to 20/200 ( in your situation when not wearing your contact lenses for distance vision).