I would pick a spot that is smaller than your chin as an anchor point. I use my middle finger/middle knuckle against the bottom portion of my right ear as an anchor point. Try to make it smaller and more consistent and see if that helps.
If that does not work and your groups are still all over the place it might not be you but your bow set up.
If it is the bow set up a bunch of things could be happening.
Poor arrow selection: Weak or too stiff of a spine, normally a weaker spinned arrow (too light) will cause erratic flight.
Arrow clearance: Your arrows could be hitting the rest funny and causing them to fly inconsistent
Out of tune, Un-timed Cams: If the cams of the bow, if it is anything but a single cam, might be out of sync causing one cam to come home quicker than the other which throws the arrow off since one portion of the string is ahead of the other.
These are a few things to be looking for. If you have been shooting a while and are still inconsistent it might be a good idea to take it to an Archery Shop (small business, avoid box stores like the plague) and have the owner look at your shot and your bow to see if something is not acting up.
Also for target shooting, to tell that I am staying accurate and to help alleviate potential problems is to try and shoot one arrow at the bullseye. If that arrow let's say hits low and left 2 inches I aim exactly at the arrow I shot into the target. If I hit right on against the arrow that I shot I have a pretty good idea that it is not the bow but me, the shooter. Just little tricks to help us figure out what is going on. works for some and other things work for others.