PPI on CAR HP

but I do recall the salesman playing the "but what if you lose your job" card to persuade me it was important.

Which is a fair and valid approach for them to take and clearly indicates that you knew it was optional.

Can I make a complaint considering the agreement shows it as optional?

You can complain about whatever you like. That includes the colour of the carpet or the brand of coffee they use. However, if you are referring to likelihood of success then you have several issues
1 - it is post 2005 which means there will be a statement of demands and needs and a better audit trail
2 - it is 2009 which is into the period that PPI mis-sales started and wre known about so firms were generally better at this time at how they documented sales
3 - you knew it was optional and choose to buy it and you havent given any reason for complaint in your post.