Your script is pretty close, you just need to set up the desired response properly. However, you could take advantage of the pattern plot to plot the pattern for a planar array.
Hope this helps,
N = 8;
M = 8;
URA1 = phased.URA('Size',[N,M],'ArrayNormal','z');
pos = getElementPosition(URA1);
% position of elements
ang_i = [-40 -20 10;10 20 -10]; % interference angles
ang_d = [0;0]; % desired angle
Rn = sensorcov(pos,ang_i,db2pow(-40)); % Noise covariance matrix
sv_c = steervec(pos,[ang_d ang_i]); % Linear constraints
r_c = [1 zeros(1,size(ang_i,2))]'; % Desired response
w_lcmv = lcmvweights(sv_c,r_c,Rn); % LCMV weights
pattern(URA1,3e8,-90:90,-90:90,'CoordinateSyste','Rectangular',...
'Type','powerdb','Weights',w_lcmv);
view(0,90);
