Learn Italian: Ero così goffo che ho fatto più pasticci di quanto pensassi. - I was so awkward that I made more messes than I thought.

Yes, absolutely. You could say Ero talmente goffo che... and it would mean exactly the same thing. Both così ... che and talmente ... che are used to express a result or consequence.

Why is pensassi in the imperfect subjunctive?

In Italian, when you make a comparison using più ... di quanto or meno ... di quanto (more or less than what...), the verb that follows must be in the subjunctive mood. Since the main action happened in the past (ho fatto), you need the imperfect subjunctive pensassi rather than the present subjunctive pensi.

Why use di quanto for 'than' instead of che or di?

You use di quanto (or di quel che) when comparing a noun or adjective to a verb or an entire clause. Here, you are comparing the noun pasticci (messes) to the verb phrase for 'what I thought' (pensassi).

Why does the sentence use Ero (imperfect) for being awkward, but ho fatto (passato prossimo) for making messes?

Ero describes an ongoing state or condition in the past (being awkward), which is the classic use of the imperfect. Ho fatto describes specific, completed actions (making the messes) that resulted from that state, so it takes the passato prossimo.