Contribution made by me (besides my employer) to RPP (Per Great-West Life, 2018 report) is not correlated to T4 [box 20, line 207].

Since my contract says that employer will equal to my contribution up to 4%.
So I contribute 4% and my employer contribute 4% as well.

When I compare the Contribution made by me (besides my employer) to RPP (Per Great-West Life, 2018 report) it is not correlated to T4 [box 20, line 207] amount (almost double difference).

Does all this information contain in my T4 [box 20] slip or should I fill my contribution part to RRSP/PRPP form page?

Or maybe I can input my total contribution to T4 [box 20] from Great-West Life, 2018 report (instead of T4 slip information)?
Cause based on: CRA web site: Line 207 – Registered pension plan (RPP) deduction

"Completing your income tax and benefit return
On line 207, enter the total of all amounts shown in box 20 of your T4 slips, in box 032 of your T4A slips, or on your union or RPP receipts"