I started sleep training at the same age, and remember it was frustrating, because I spent 1 hr with the shpat. I quit for two weeks and did AP, and then started again with the shpat when he was 10 weeks, and now my lo is 14 weeks old, and I have to do very little shpat! I just put him down after our WD routine and place my hand on his chest, and he closes his eyes. I leave the room at that moment. I don't have to wait the 20 min. Trust me, you will get there!
Just don't worry if sometimes you use AP for getting him to sleep longer. Your lo is sooo young, and he will learn it, but just give him time!! My advice is not to worry so much, you will have lots of time for sleep training! And as he grows, things get easier!! Hang in there!
I would also do some AP so that he catches up on his sleep for several days. You can use this days to get to know your lo better!!