Fourier transform of a Gaussian in Excel returns imaginary coefficients
A delayed or offset Gaussian would have complex coefficients. I suspect that the $x=0$ point you are assuming is not where Excel assumes. The magnitude would have a Gaussian shape and the phase would be Linear,  which you can use as a diagnostic. Gaussian is also infinite in extent so, there is going to be some effects due to truncation.  

The issue that confuses most people is that the DFT has the character of "assuming" that it is operating on one period of a periodic sequence. In your case the Gaussian is symmetric around $x=0$ but the first point in the sequence corresponds to $x=0$ so where do the values for $x&lt;0$ go? They go with the next cycle of the sequence so if the period has $N$ data points, depending if $N$ is odd  or even the periodic portion corresponding to $x&lt;0$ would be in the samples from $N/2$ to $N-1$.