I take a cardboard box and cut a V on the two opposite sides when I did not own an fancy gun rest. Put the rifle in those V's and remove the breech plug. Now I like to line up at 13 yards, on a door. A hallway works great for that. Put a flashlight on that door if you have to. Remove the breech plug and without touching the rifle, look through the barrel at the door. If you can aim it at a door knob ... all fine and good. If not, take some masking tape (so you don't hurt the door paint or finish) a put that tape on the door in the center of where you see through that breech plug.

Then carefully look through the scope and start to make adjustments to that tape. After you have the two lined up. Go to the range and shoot at 13 yards and shoot the first shot, then move to the bullet hole. Shoot a couple and they should stack.

This should put you very close at 100 yards by the way. Although if you mount the scope properly, at 13 yards you should be pretty close.