Short answer. Just your pro rata share, generally. Article 1825 provides that when no actual partnership liability results from the misrepresentation, the person who made or consented to it is liable pro rata with any other consenting persons, or separately if there are none — not for the whole debt as if a real partnership existed.
What the law says
(1) When a partnership liability results, he is liable as though he were an actual member of the partnership; (2) When no partnership liability results, he is liable pro rata with the other persons, if any, so consenting to the contract or representation as to incur liability, otherwise separately.
Civil Code, Article 1825 — Partnership by Estoppel. Read the full provision →
The two outcomes Article 1825 distinguishes
Article 1825 addresses what happens when someone represents themselves, or lets someone else represent them, as a partner to a third person who then extends credit on the strength of that representation. The article then draws a sharp line between two different outcomes, laid out as two numbered rules: (1) when a partnership liability results, he is liable as though he were an actual member of the partnership; (2) when no partnership liability results, he is liable pro rata with the other persons, if any, so consenting to the contract or representation as to incur liability, otherwise separately.
When a real partnership liability does result
Under the first outcome, if the misrepresentation actually produces a genuine partnership liability — for example, because all the actual partners consented to the representation — the person making the representation is treated exactly as if they were a real partner, which under partnership law generally means being liable along with the other partners for partnership debts, not merely for a fractional share.
When no real partnership liability results — your situation
Your situation falls under the second outcome instead: no real partnership liability resulted from your misrepresentation. In that case, Article 1825 makes you liable pro rata with any other persons who similarly consented to the misrepresentation, meaning liability is divided proportionally among however many people made or consented to the representation. If you were the only one who made or consented to the representation, the article says you are liable separately — for your own portion, on your own, rather than for the entire debt as one person.
Why the article treats these two outcomes differently
The distinction exists because the two outcomes reflect genuinely different situations. Where a partnership liability actually results, the law treats the represented partner the same as a real one, with the consequences that follow from real partnership membership. Where no such liability results, there is no actual partnership to attach full partnership-style liability to, so the article instead spreads liability pro rata among those responsible for the representation, or holds a lone representer separately for their own part.