correct way for zero padding

Here in the code below, I am taking fft of my data and plotting it. Moreover, I am doing zero padding by multiplying the signal length by 1000.

Is it the correct way for Zero padding? Moreover, am I defining frequency axes correctly? I am not getting desired output. Thanks everyone in advance

   % second-order butterworth
    [b, a] = butter(2, [w1 w2], 'bandpass');

    load('fb2030');                                   % loading the data
    x = fb2030(30,:);
    % filtering
    y_filt = filter(b,a,x);                           % filtering the received signal
    nfft = length(y_filt)*1000;                       %%%%Zero Padding
    res = fft(y_filt,nfft)/ nfft;                     % normalizing the fft 
    %    
    f = fs/2*linspace(0,1,nfft/2+1);                  % choosing correct frequency axes
    res = res(1:nfft/2+1);                            % amplitude of fft(taking the half length of nfft)
    figure,plot(f,2*abs(res));
    xlabel('Frequency in MHz');ylabel('amp')

[dpb]

By nfft = length(y_filt)*1000; you've caused a length of 1000X the actual length of your signal so only a small fraction N/(N*1000+N) or just under 0.1% of the signal being transformed is nonzero.

The typical zero-padding is to the next power of 2 over the length but that is mostly a remnant of years ago when compute power was much less and the difference in speed of the algorithm was a serious concern. Now if the signal is of sufficient length to have reasonable resolution, you may well do without padding at all.

But see

doc fft
doc nextpow2

for sample of doing a PSD