Immigration form I-864 Question 8?

I am US citizen sponsoring my mother to get her green card and I am filling I-864. I don't have enough income so my spouse is also filing I-864a so both of our income is combined for sponsorship purposes. In my I-864 form Part3. Question 8 asks if "I am sponsoring the principal immigrant named in Part 2 above" it has check mark as well as following check mark boxes for Yes and No answers. I am ticking the primary question's box as well as Yes answer. Since we are not joint sponsors. I don't have any one else included as beneficiary in the affidavit. Am I filling correctly? Thanks for your answers.