You can't zoom the Real-Time Preview window (although you can resize it). Define one or more previews in your image covering regions of interest, which you can select in the RTP. By defining relatively small previews, you can easily achieve the desired zoom ratio on RTP.
Besides the RTP, becoming fluent with the use of previews is very important to get the most out of PixInsight. Previews are powerful and extremely flexible tools to try out processes.