Is the I/Q data 16-bit integer or are you using the 32-bit floating point data from the API? If you are using the 16-bit integer data, there is an additional scale factor you must account for.
Also, what value are you comparing it to in Spike? If you are looking at a modulated signal, you’re going to need to do a channel power measurement. If looking at a CW, then the instantaneous I/Q power will have more relevance.
dBm = 10*log10(i^2 + q^2) is the correct equation. Make sure it’s log10 not log2.
Look forward to your response.