Adding an EV Charging Station to an AC Circuit
Nope. EVSE's need to be on a dedicated circuit.  That's a Code requirement. 

The amps of the service don't decide how many spaces are in the panel. "spaces" and "amps" are totally different numbers, you can have 12-space 200A or 42-space 100A. It sounds like you need to add a subpanel somewhere convenient.  I recommend counting the spaces (not circuits) you now have, subtract that from 50, and get a subpanel with about that many spaces.