Electrical – Constructing Bode plot from experimental data and constructing a transfer function

I've been trying for a few days to convert an experimentally obtained (frequency against magnitude and frequency against phase) graphs to a Bode plot and then construct a transfer function from the Bode plot

I constructed a table:

1. Converted each frequency from Hertz to rad/s by multiplying it by \$2\pi\$
2. Converted each magnitude to dB by multiplying it by \$20\log(\text{magnitude})\$

Note: As seen in the original graph, all the magnitudes are negative. When converting to dB, you cannot take the log of a negative number so I assumed it to be positive. Am I correct? Will this affect my Bode plot?

The table can be seen below:

Then I plotted the Bode plot below:

I understand that my transfer function will be a first order because the phase shifts 90 degrees meaning the highest power of the denominator will be 1. In other words, there will be 1 pole in the denominator.

In summary, my questions:

1. Was I correct in converting the negative magnitude to db by ignoring the negative value?

2. What will be the final transfer function of the constructed Bode plot?