Yes you are right - Registax is more for planetary work - use instead
DeepSkyStacker which is freeware; and read the guide/help; in fact the default settings in the software allows you to get pretty close good results right off - indeed you should try to "stack" more subs to get better results
From the little I can see from your image - tracking seems alright for a 6sec shot though exposure could be more - 30secs or more would capture far more details etc
HTH
Cheers
Bill