CSI of the guard-band subcarrier in 5G channel

my ultimate goal is to use 5G toolbox to estimate the compete channel response (for in-band subcarriers & guard-band subcarrier).

This can be done as follows

1. Generate 20 MHz signal
2. Use of an array with Nt antennas at TX
3. Perform perfect channel estimation

I can use the following link to generate 20 MHz signal. But not sure how to check the number of subcarriers or IFFT point

https://www.mathworks.com/help/5g/ug/5g-nr-tm-waveform-generation.html

The following link perform perfect channel estimation. But I have question why the number of subcarriers in the channel magnitude response is limited to 300? what about the rest of subcarriers

https://www.mathworks.com/help/5g/ref/nrperfectchannelestimate.html#mw_function_nrPerfectChannelEstimate_sep_mw_3cbeae39-cf8f-4ffc-8cd5-1049e2c6108b

Is it possible to use 5G toolbox to estimate the compete channel response (for in-band subcarriers & guard-band subcarrier)?