Heptane is a non-polar solvent, while hydrochloric acid (HCl) is a strong polar acid. When you have a solution of HCl that is saturated in water, heptane will not effectively extract the HCl because heptane is not a good solvent for polar substances. The HCl will largely remain in the aqueous phase due to its high solubility in water and the polarity of the acid.
If you're looking to extract HCl from an aqueous solution, you would typically use