If I have a company group RRSP with 50 50 matching, do I input my T4 as is (box 20) and the full RRSP receipt (full amt.) or subtract 50% of that amt. in receipt section?

You would enter the T4 info (box 20) as is, and then the amount that you (and not your employer) contributed to the RRSP. We recommend using Auto-Fill My Return and then verifying that everything turned out as expected.