Wait and see what the situation really is - things can't be that bad!
After one month you realise that the former manager was not exaggerating, the volunteers are not very reliable and seem to resent you. It seems like you have a crisis situation on your hands.

What do you do?

1. Start recruiting new volunteers
   
   
2. Fear that you've made a mistake taking on this challenge
   
   
3. Call an emergency meeting of the Management Committee (MC)