FFT to IFFT issue with going back to time-domain

Im trying to obtain displacements from frequency response function (I have data for acceleration and force) and with that information to obtain displacements by going back to time-domain with IFFT. I have issues with inverse Fourier transform, I know that I need some pre-conditioning regarding sizing but I couldnt find the solution. I get like mirror-image of the signal when I use ifft. I provided the code and functions for frequency response function along with data. Any help much appreciated!

Main Code:

file='accela2.txt'

data =load(file);

acc_1 = detrend(data(:,1)); %Acceleration is in g's

force_1 = (data(:,2)); %Force is in Newtons

Fs=1000; %Sampling Frequency (Hz)

%-------------Using My_FRF function to get FRF-acceleration---------------%

time=linspace(0,3,2049); %FRF  function produces a vector (therefore size 2049)

[freq, HaMag] = My_FRF(acc_1,force_1,Fs);  %My_FRF function - acceleration

FRFaccel=HaMag

% plot(freq,FRFaccel); xlim([0 30]); %Check on FRF graph

%--------Calculation of Radial (Force) Frequency-My_FFT function----------%

%Use Force_1 and Fs as input in My_FFT --> get force_1 frequency (f1)

%Multiply f1(omega) by 2*pi to convert to rad/s 

[f1,m_wave1, psd_1] = My_FFT(force_1,Fs);

omega=transpose(f1).*(2*pi); % Hz to rad/s for force frequency

%----------------FRF-Displacements(from Acceleration FRF)----------------%

   FRFdisp=FRFaccel./(-omega.^2);

   FRFdisp=abs(FRFdisp);

   Disp=ifft(FRFdisp);

figure(1);

plot(time,Disp);
xlabel('Time(s)')
ylabel('Displacements(m)')