Until when is a cold sore contagious. my scab came off 2 days ago and i just have a scar?

No longer contagious: You're probably no longer contagious. Herpes lesions such as oral cold sores have active virus only the first few days; once healing is well underway, transmission risk is very low. But to be safest, it's best to do just as you have: assume you are contagious until healing is complete, i.e. the scab falls away by itself. A pink "scar" (which will fade) isn't infectious.