>I don't think I have those
Head back to Oleg's outpost. Make sure you've saved Jhod the cleric. He's at thorn ford. If you didn't already, go back there and kill the bandits, then talk to him. Afterwards he will tell you to meet him at Oleg's Outpost. That's who you buy the scrolls from. You need Delay Posion communal and Protection from Acid communal.
>Problem is that the big one has a pretty powerful projectile attack too
There's a tight pathway you can use as a choke point. It will allow you enough time to kill off the weak centipedes before the big one gets into the fight. Here's the choke point in question:
Thanks, the positioning around the chokepoint was key. That and spamming Elemental Ray, Acid Splash and Burning hands with my sorc. I did not end up going back for the items you've mentioned, kind of regretting that now. Those things drained the shit out of my dex. I rested, used all my restoration potions and used all my available Lesser Restoration spells and I still have some drain left.
You. Don't. Have. To. Fight. Everything. Right. Away.
Normally I'd agree with you, but time limits generally make me nervous. I really don't want to waste time walking back to Oleg, resting up and stocking up. I know I'll need to do that sooner or later, but ideally I want to finish up this Tartuccio quest first.