Well that is something you should have addressed there and then , or at least not signed it , if you signed it you must have agreed with what was written .Remember you cannot be forced to make a statement .
The problem with persons making their statements themselves is that if a court case is required most of their evidence is written of as inadmissable as it doesnt conform with the rules of evidence and then you lose the case or the potential evidence . You may not particualrly like the person taking your statement or the organisation for which they work , but as said it is voluntary and you can say what you want and do not have to sign anything .
Remember in court its your statement and your signature .
Read thoroughly what you have dictated and only sign it if you are happy
Accurate if rather naive.
3. Only put in a statement what you are prepared to swear under oath as fact.
I think you will find the witness statement must include a statement of truth in any event under civil rules.