Ok, then don't bring crappy pokemon. lol. Mine were around that level too, and I had crappy pokemon with me.
Bring a ton of hyper potions and you should be fine.
Giratina is a bitch to catch, btw. I went through about 8 ultraballs(and then 5 or maybe more other random pokeballs). What worked for me, the down b trick... lol. No one even knows if it's fake or not, but I swear by it XD. Also, make sure to put it to sleep.