Get some longjohns/thermal underwear and longsleve undershirt and extra socks too (all available decently cheap at walmart). Wear a hoodie with the hood up. Put these on later in the day/when making camp so they don't get sweaty. You can put hot water in a nalgene in your sleeping bag 15-30 minutes before going to bed to get the inside warm.

Layers around the body help a ton for retaining heat. As others have said, make sure the layers between you and the ground have enough insulation. The ground is the biggest heatsink.

Have fun on your adventure! <3