As I already wrote in the foregoing threads, it would be necessary to have a parameter for scaling in x/t-direction. This would be a factor of x in your function Function() which is not present. So again, with the function you provide, a good fit will not be possible, I guess.
In the attached file I simply added a third parameter ag2 as a factor of x and got a much better fit. I think you should be able to get rid of one of the other parameters, using a fit function with two parameters only as in the foregoing threads, but I didn't bother doing so.