Amplitude of frequency bin in FFT doesn't match time-domain amplitude
You seem to know how to handle the DFT/FFT scaling so that its output matches the
sampled signal's power/amplitude levels. 

Yet there is a discrepancy between your expectation and the obsevred DFT result? There are a few reasons. Your assumptions on the sampling rate or the signal frequency could be wrong. Indeed as it seems from your figures, the signal is not a pure sine wave. In that case the amplitude looses its crisp definition and spectral leakage and main lobe width smearing becomes an issue. For details please search the site for spectral estimation, spectral display etc...

For your convenience, I have produced an ideal case to your description with MATLAB / OCTAVE code. I'm getting exactly what is expected. So this suggests me that your signal is not a pure sine wave. It's either modulated, or your sampling rate and frequency information is not consistent.

clc; clear all; close all;

T = 0.0225;     % observaton interval in seconds
f0 = 750;      % sine frequency in Hz.
Fs = 357E3;     % sampling frequency in Hz.

t = 0:1/Fs:T;   % analog time

N = length(t);  % number of samples taken...

A = 1.5;        % amplitiude of the sine
x = A*sin(2*pi*f0*t);   % sampled analog signal...

figure,plot(t,x);
title('Analog current waveform');

M = N;          % DFT length (mostly equal to sample size)
X = (2/N)*fft(x,M);

f = linspace(-Fs/2,Fs/2,M); % analog frequenc range in Hz.
figure,stem( f , abs(fftshift(X)));
axis([-1500 1500 -0.1 2]);
title('FFT magnitude of the obtained samples');


The resulting figures are as follows: