Answer by Wray Rives:
Your first problem is as others have noted the IRS is not going to automatically adjust the tax return you filed for yourself, just because you sent them a 1099. You will have to file an amended return.
Your possible second issue may be more important, because you refer to this person as your "business partner". Business partner has a very different meaning in tax reporting than independent contractor who you the business owner paid for performing services.
If this person is truly your partner in the business, then you should be filing a partnership tax return and splitting the profits or losses among the partners. This individual does not have to have an ownership interest in the business and could very well be considered your "partner" if they simply have a right to receive a certain portion of the profits from the business.