What do you call "Baseline correction" in the case of resting-state recordings?
If you applied a band-pass filter at 7-13Hz, then your don't have any "DC offset" to remove.
the source map i am getting is not showing any cortical activation
You probably just have to change the amplitude threshold in the Surface tab.
If you are not familiar with this, I'd recommend you start by following all the introduction tutorials, using the example data provided instead of your own recordings. Then make sure you also read the tutorial "EEG and epilepsy" for instructions specific to EEG data.
https://neuroimage.usc.edu/brainstorm/Tutorials
Note that units "10^8" in the colorbar legend are very suspicious.
You may have units errors in your EEG recordings.