By Sarah Lumley One in three small business owners are feeling stressed about how well their business will perform this Christmas – with 21% saying this could define their growth for the next 12 months. A survey of 500 business owners found that 60% believe the weeks leading up to Christmas are their most important period of the whole year – with 58% worried about what low sales in December could mean for the year ahead. And three in 10 (29%) view the festive season as their biggest opportunity to make money, with 32% saying their Christmas revenues help to tide them over during quieter months…