Question: 3D fit question

I have a set of 3D data points that I'm trying to fit to a f(x,y) mocel and I do not know how to fit the data to the model. I am using the statement

g:=Fit(a+b.x+c.y+d.x^2+e.x.y+f.y^2, x,y,z,[x,y]);

where x,y are the independent vairables and z the dependent variable that I'm trying to fit.

My problem is that I have the error message

Error, (in Statistics:-Fit) invalid input: Fit expects its 4th argument, v, to be of type {name, list(name)}, but received [.686, .693, .702, .714, .728, .745, .764, .785, .594, .597, .601, .607, .614, .621, .63, .641, .545, .546, .549, .553, .557, .562, .566, .574, .514, .515, .518, .52, .523, .526, .53, .535, .494, .495, .496, .498, .5, .503, .504, .505, .479, .48, .481, .482, .484, .485, .488, .49]

Does somebody know what I'm missing or doing wrong?

Thanks