Did you drink the Mongoose Potion just before the fight starts? That is essential if you want to defeat it. Drink the Swallow potion to regenerate Vitality (health) quickly. Meditate to drink both these potions. Go to the Alchemy section and make them if you haven't already.
If you stop for a while, he smashes one of the gooey tentacles on that spot, so keep an eye on it, set a trap using Yrden sign and get out of the way quickly. When the tentacle hits the ground, it'll be trapped, you then have to hit the gooey part to cut it off. The rest is just dodging. Do it 3-4 times and you should figure out the rest. Its easy afterwards.