Construct IFFT from only the major frequencies of an input signal?
Without having the original data it is difficult to confirm, but the DC offset is due to bin 0 in the DFT. Bin 0 corresponds to the DC term or average offset value for the sequence. The plot in the DFT result shows a large value for bin 0 while the time domain waveform appears to be closer to 0 average. I would need to see the original data to determine how the DFT bin 0 occurred.

Update: Upon reviewing the original data from the OP, the average of this data is 0.4123 which is consistent with the result achieved.