What are the DOs and Don't in meeting with the top management of the Client?

Context   (Selling a Product or Service)

Hi,

I am preparing for my first official meeting and close the deal with the top management of my prospect.

My product is SaaS product. I know the features level and little bit of technical aspect. I am the first person to contact for my product and I did many online demos as well. The second level is the Technical section, which will handle by my manager.

This prospect wants a face to face meeting. My manager is unable to attend the meeting. So the next best person knowing about the product is me.

I want to go and face it. But little nerves. What if they ask too much technical questions? If they have suggestions or customising requirements, how to tackle it? Most importantly, the commercial part. If they have some different opinion or suggesions, how to handle it and the final result will be WIN-WIN for both of us? These type of questions are disturbing me.

One thing for sure , I AM GOING!!!!

I don't want to tell them,let me ask my manager and update you. or I don't want to make a situation of- Hey, you are not the guy we wanted to meet.

Help this nerves first official trip guy...

Thank you...