Matlab code for finding prime numbers

I wrote a code for the sieve of erasthosenes (a way to find and arrange all the prime numbers before a user-defined value, "n", both by dividing the numbers by all the pervious numbers, and by only going up to the square root of n), but the grader was not satisfied with my code. I'm not sure what I did wrong to his eyes. Any ideas? Please and thank you!

function p = prime_seive(n)

p = [0 2:n];   
for k = 2:sqrt(n)
    
if p(k)   
p(k^2:k:n) = 0;

end
end
p = p(p ~= 0);
end