Bad grades are bad grades. You may need to move schools or u may need to work harder.
If your bad grades are down to the fact that the standard of teaching is lousy and the subjects are not being covered or explained properly - and that's what's making it a "bad" school - then no, it's not really your fault. But if they're caused by being allowed to misbehave and not pay attention in class, and getting away with not doing the work properly, then they're at least partly your fault - because you could do better if you wanted to.
Well, school is about everyone but grades are individual - it should still depend on your ability. If you're easily influenced your grades won't be that great in a bad school, but if you realise school is a selfish thing, you need those good grades no matter what environment you're in, good or bad, you will get them. Good school or bad school, you need to put the same hard work in!