"not a bit" means "not at all" while "
not a little" means "very,quite,much or a lot".
not a bit的意思是“一点也不”,而not a little的意思是“非常,很,十分；许多”.再如：
I'm not a bit hungry tonight.今晚我一点也不饿.
I'm not a bit cold.我一点也不冷.
He was not a little surprised.他感到十分惊讶.
He was not a little tired and fell asleep quickly.
他非常疲倦,很快就睡着了.
It has given me not a little trouble.这给我带来许多麻烦.
He spent not a little on clothes.他买衣服用去许多钱.