Remove Aliasing in a signal

In my code I have a cosine function that has a frequency of 466.2 Hz, and I'm doing an FFt to remove content that is under 2000 in magnitude. Then I'm doing an ifft of the new signal, and using a low-pass filter to try to remove any aliasing in my signal, but I still end up with aliasing.I'm pretty new to signal processing and I'm not sure what I'm doing wrong here any help is appreciated. Here is a picture of my original signal and a picture of the aliasing.

ts=0.000001;   
Fs=1/ts;   
n=[0:7000];
bflat4=466.2; %frequency of B-flat
ynote1=10*cos(2*pi*bflat4*ts*n);
yfft1=abs(fft(ynote1));
ycomp1=yfft1;
for k = 1:7001
     if ycomp1(k) < 2000
          ycomp1(k)=0;
     end
end
ynew1=ifft(ycomp1);
plot(ynote1)  
%plot(ynew1)
%sound(ynote1)
[b,a] = butter(1,bflat4/(Fs/2));
yfilter = filter(b,a,ynew1);
plot(yfilter)