I recommend you go new document and search for a template toc. Then you can change it as you will to your liking. I found one called "Table of Contents (Distinctive design)"

To create one by hand continue as you were but to add a sub header toc just tab in the necessary spaces.

Set everything to be on the left hand side and it will work for you.

Below is the example I found in Microsoft templates. You can copy it and then modify it to suite your needs.


TABLE OF CONTENTS
Chapter 1_________________________________________________ _____________ #
Section 1.1_______________________________________________ _____________ #
Subsection 1.1.a_____________________________________________ ___________________ #
Subsection 1.1.b_____________________________________________ ___________________ #
Subsection 1.1.c_____________________________________________ ___________________ #
Section 1.2_______________________________________________ _____________ #
Section 1.3_______________________________________________ _____________ #
Chapter 2_________________________________________________ _____________ #
Section 2.1_______________________________________________ _____________ #
Section 2.2_______________________________________________ _____________ #
Subsection 2.2.a_____________________________________________ ___________________ #
Subsection 2.2.b_____________________________________________ ___________________ #
Subsection 2.2.c_____________________________________________ ___________________ #
Section 2.3_______________________________________________ _____________________ #
Chapter 3_________________________________________________ _____________ #
Section 3.1_______________________________________________ _____________ #
Section 3.2_______________________________________________ _____________ #
Section 3.3_______________________________________________ _____________ #
Subsection 3.3.a_____________________________________________ ___________________ #
Subsection 3.3.b_____________________________________________ ___________________ #
Subsection 3.3.c_____________________________________________ ___________________ #