Hello Anonymous,
Sorry to hear your struggling. You're in year 11, what's the worst they can do if you do not attend?
Even if you didn't attend for no reason, they can't punish you at this stage.
3 days is enough, but depends how you use it.
Also, remember, grades don't determine your worth, they're a memory test, whatever happens, happens. If you know you tried your best, why be angry at yourself?