How to fix a function to get 2d integral

Hello, I am trying to use the built in function integral2 to compute an area.

However, I am getting this warning 'Reached the maximum number of function evaluations (10000). The result fails the global error test.'

My function and the integral doesn't seem so difficult. The function is continuous. Does anyone have any ideas as to why this is happening?

Here is my code, the image generated at the bottom is just to give an idea of what the shape looks like.

a=-5.0;
c=-0.4;
e= 1.1;
L= 50;

fbonus = @(z) (1 - tanh(10.*(((2*abs(z))./L).^8)));

b0 = -8.0;
d0 = 0.2;

b = @(z) b0 .* fbonus(z);
d = @(z) d0 .* fbonus(z);

yfunc = @(x,z) real((a*sqrt(1-((x./b(z)).^2)) + (a/2) .* sqrt(1-((x./(2.*b(z))).^4)) + c .* exp(-abs(x)./d(z)) + e));

Q = integral2(yfunc,0,15,0,25)

Qtotal = Q .* 4;

y = zeros(37,51);    

for i = 1:37;
    x = i - 19;
    for ii = 1:51
        z = ii-26;
        y(i,ii) = yfunc(x,z);
    end
end

figure(1);
surf(-25:25, -18:18, y);
title('The Boat'); xlabel('length, z'); zlabel('depth,y')
ylabel('width,x')
colormap(spring);

Thank you for the help!