the BET graph you share have a little problem that may be due to water molecules in your sample (not fully dried) or not uniform (if powder try to grind properly) or may be because of your sample stuck on the side of glass tube ( this need expert person to do) i will recommend to do again if possible try with another BET machine
I'm not sure because I don't use the same equipment but, it seems that you attempted to fit the all P/Po range which is not appropriate for the BET model (usually 0.1