Signing a document under duress.

I was working for this company, and was asked to sign a piece of paper, I was told it was about the meeting we were going to have and this document should of been attached to the contract(I did not sign no contract). I was told that the peice of paper was about me not repeating anything in the meeting and not to tell anybody what the company was about. Prior to this meeting I questioned the company about my wages, the owner of the company telephoned me and asked me to bring my kit with me when I was coming down for the meeting. I asked if she was sacking me, she told me no and that we would speak later at the meeting. When I arrived at her house, this was when all the above happened. I had been working for her for 2months prior to this. and no contracts were signed during this period. She told me that I had to go because she implied I had to many personal problems and it was evident it was effecting memy work. I totaly disagreed with her. I feel I was too upset and that I was taken advantage of when signing this document.
What I need to know is - I am thinking of starting a business up doing a simaler programme., but I am very concerned about this document that I signed, I have asked for a copy of this and I received it by email, I have noticed that several lines have been added to this document, and I feel this was not the original document that I signed. This document that I have a copy of is stating that I must not attempt to create or a variation or derivative of this programme any where in the U.K. or let others know about the contents of this programme. I would be very grateful if you could let me know as soon as possible, if I would be allowed to set up my own bussiness doing a simular programme, as I have already approached a bussiness centre on this matter.