I had my third sparring session yesterday (all punches to the head only were allowed).

The problem is my opponent (short inside fighter) would slip to my right get inside and start unloading. Before I started sparring I always practised the shoulder roll at home. Now that I have started sparring my trainer does not want me to use it because he believes its too advance. He wants me to stand my ground and double guard. I did that but I haven't trained to fight on the inside. I waited for the punches to stop but they didn't. Without thinking I turned away as if I'm shoulder rolling but its as if I'm caught with two minds. I turned away without raising my shoulder and with a double guard getting hit in the process. My trainer stops the session saying I'm gonna get myself knocked out.

My question is how do I fight on the inside with a double guard. Once they are inside do I step forward stand my ground or step back? Do I put my weight on my front foot or on my back? Do I plant both feet or still keep my rear heel slighty raised? How far apart should my legs be? And what are some basic combinatons I can use to punch my way out? I'm 73 kg at the moment but will prob fight at 69 kg, about 5'10", very skinny weak upper body build for my weight, but very strong legs, very fast and have a big right hand. Thanks alot and I would really appreciate it if you could help me.