First of all, you signed the contract on behalf of the company manager. If the company authorizes it, it is an agency act in civil law, and the consequences of the contract will of course be borne by the client. If the company is not authorized, it belongs to the agency by estoppel, and the company should also bear the responsibility.

For the contract itself, whether you are authorized or not, your signature instead of the company seal will not affect the validity of the contract.

To put it simply: the contract is valid, and if the contract is profitable, you have something to recommend it; If the contract causes disputes, you are not at fault.

But whether you have violated your company's internal regulations depends on your company's internal regulations.