So I've got my navigation log mostly filled out. All that's left to do is determine fuel to climb and descend. I go to my Archer POH (Pilot Operating Handbook) and use the time, fuel, and distance to climb and descend charts. Got about 1.5 gal for both descent and climb. 8 min and 6 NM for climb, 8 min and 18 NM for descent. What do I do with these numbers?
Realize that both the climb and descent are taken from the en-route section.
I always calculate climb first and determine where I will reach top of climb on the sectional chart. I then calculate descent and figure out when I need to descend on the sectional chart. The distance in between is my en-route section.
From reading your question, it seems you calculated en-route from departure airport to destination airport. You don't want to do that.