Next time, share your code so that we can debug your code. My guess is you angle are from +90 degrees to -90 degrees instead of 0 to 360 degrees.
Here is a simple circle code;
q = 0:0.01:2*pi; % angle 0 to 360 degrees in radian
r = 10; % radius
x = r*cos(q); % cartesian x coordinate
y = r*sin(q); % cartesian y coordinate
plot(x,y)
