How likely is it to have a life threatening reaction to the covid vaccine after about 3 days of getting the first shot? such as blood clots or maybe getting bells palsy?

Based on what we have experienced or seen so far the probability is very very low. Most serious reactions have occurred during first 48 hours . Different individuals react differently to different vaccines , Including Flu vaccine. Putting in perspective the serious side effects versus the benefits , it's wiser to take the vaccine.

Would not expect at this point, for you to experience any new problems and you are pretty much past any critical risks. The severe problems like myocarditis are very rare, seen so far with just the J&J jab. Bell's palsy would not be caused by the vaccine as it appears due to herpes simplex or zoster.