Ok! First of all, thanks for answering! 
then, the correction on f2, starting the parameters at [0] solved the problem of having too many parameters, I guess it supposed that there were other parameters in the function, though I didn’t write them. And also I agree that the errors are not taken into account, as I fixed the parameter, sorry, now aI put the errors somehow setting the parameters in a limit limitted by its error (SetParLimits(par, value-error, value+error). So thanks again for everything!!