Have I used polyfit/polyval correctly

I am just trying to get used to the polyfit and polyval function.

My question says to use the polyfit and polyval functions to approximate price for N=1 N=5 N=10 and plot the approximation

I have my data file as a 15x5 double with prices being the 5th column day being the first column. I have written.

day  =  Data(:,1)); %first column of days
price =Data(:,5) ; %data we want to approximate
T = table(day, price); %create a table for easier computation

for i=[1 5 10] %N values
    [p,~,mu] = polyfit(T.day, T.price, i);  
   f = polyval(p,day,[],mu);
plot(day,price) %plot of prices
hold on
plot(day,f) %approximation plot

end

Im just wondering if I am correct in how I have done that. the approximations seem in line with the graph but I cant see were I've approximated price