Extrapolation for a contour plot

Hi, I have a table XYZ named p3d with three columns (xyz) as below:

2139.36236643955	1206.78565433912	3
2066.17058682721	1205.71920426345	4
1992.97880721486	1206.78565433912	4
1902.70894569297	1209.98500456615	-4
1806.33976920338	1208.91855449048	-14
1720.06006488482	1209.65685130956	-45
2045.27086002642	1431.37983116559	-9
2090.50691274803	1361.30522065203	-7
2124.63235602924	1316.20769903440	5
2165.10671899068	1266.94732926745	-5
2267.67427744254	1099.98622837556	-17
2119.82902977040	1107.47909052381	-14
1940.91485323962	1107.47909052381	-7
1932.34411424413	1016.62813697632	-13

and want to visualize data in such a way:

I've interpolated my data with griddata, but it doesn't have extrapolation method. Command griddedInterpolant can do this, but it demands matrix for 2D case - and I have only vector.

Is extrapolation of data from correct way to obtain desired values?

How can I restrict matlab to plot in a redundant area?

How to overlay background image and a graph (now graph is just over the background)?

Now my code is:

img_an = 'KSM11.png';
img = imread(img_an);
limits = size(img);
% Draws initial grid maximizing its size
sz=get(0,'ScreenSize');              
fig=figure('position',[sz(1) sz(2) sz(3) sz(4)]);
xlabel('X','FontWeight','bold','FontSize',14)
ylabel('Y','FontWeight','bold','FontSize',14)
xlim([0 limits(2)]);
ylim([0 limits(1)]);
grid on
hold on
imagesc(flipud(img));

x = p3d(:,2); % first column is reserved
y = p3d(:,3);
v = p3d(:,4);
[xq,yq] = meshgrid(0:1:limits(2), 0:1:limits(1));
vq = griddata(x,y,v,xq,yq);
% mesh(xq,yq,vq)
% [xx,yy] = ngrid(x,y)
% vq = griddedInterpolant(xx,yy,v,'linear','linear'); smth is wrong

[C,h] = contourf(xq,yq,vq);   
clabel(C,h)