How to make my surface plot have symmetric centre in origo?

I have a code(I think it's easier to see what I mean if you plot it):

 % Convex
N = 100; % Even number of points
H = 0.02; % Height.
[x,y,z] = cylinder(-0.02:0.02,N);
x = x(:,1:ceil(N/2)+2);
x(:,end) = x(:,1);
y = y(:,1:ceil(N/2)+2);
y(:,end) = y(:,1);
y=y+(0.02+0.001); % Distance from z=0
z = -z(:,1:ceil(N/2)+2);
z(:,end) = z(:,1);
z(2,:) = -z(2,:)*H;
surf(x,z,y)

 hold on

 %concave
N = 100; 
H = 0.02; 
[x,y,z] = cylinder(-0.02:0.02,N);
x = x(:,1:ceil(N/2)+2);
x(:,end) = x(:,1);
y = y(:,1:ceil(N/2)+2);
y(:,end) = y(:,1);
y=y+(0.02+0.001); 
z = z(:,1:ceil(N/2)+2);
z(:,end) = z(:,1);
z(2,:) = -z(2,:)*H;
surf(-x,-z,-y) % Difference concave/convex

 axis equal
ylim([-0.04 0.04])
xlim([-0.04 0.04])
zlim([-0.04 0.04])
xlabel('x')
ylabel('y')
zlabel('z')
hold off

How can I make this centre in the middle of the y-axes, and grow in both directions if I change the height("H")?

Any tips are greatly appreciated!