Help I bought the wrong fixit (i think)

Theyre completely different. Paste is like working with soft serve ice cream, Apoxie Sculpt/Fixit Sculpt is more like working with stiff chewing gum.

I am a beginner, and don't really know what's better. Do you recommend that I to return the paste and get some Sculpt?

Everything has a use, but if you're sculpting then the paste isn't ideal. It might be good for liquid or sludge effects though.

If you're a total beginner then go buy some little bricks of Sculpey instead, theyre a cheap way to practice sculpting and can be hardened by baking. Or grab a tub of Monster Clay to practice bigger pieces, it never hardens or dries out. Apoxie/Fixit Sculpt is a terrible value for the amount of material you get, especially if you're sculpting a big statue.