Stressed about grades? ?

Basically I've just been really stressed out about my grades lately. I'm a ninth-grader and usually a straight A student and now I'm getting some Bs (especially in citizenship), and progress reports come out tomorrow, and I really don't want to face them (not to mention ruin my Halloween). I'm a perfectionist, so I'm really stressed. Any advice? I've been getting serious headaches. Thanks in advance.