You may refer to the following example to make sure your variable x,y and z are in similar format.
xcoord = 1.5:0.1:3; % x-coordinates from 1.5 to 3.0
ycoord = 2:0.1:5; % y-coordinates from 2.0 to 5.0
[X,Y] = meshgrid(xcoord,ycoord);
zdata = randi([5 30], numel(xcoord),numel(ycoord)); % Simulate the data
x = X(:); % Your varaible x should something like this as a column vector
y = Y(:); % Similar for variable y
z = zdata(:); % Similar for variable z
tbl = table(x,y,z); % Combine them in a table
h = heatmap(tbl,'x','y','ColorVariable','z'); % Generate heat map
