Couple ideads. If you are right handed, turn you head left a tad to make sure you are looking square at the target. Make sure your drawing elbow is in line with the arrow, ie pulling straight back. Make sure you are pulling through and not collapsing at release.
I am by no means an expert, just had the same problem and the foregoing fixed it (that and remebering to not jam my finger into the corner of my mouth, but just lightly touch it to confirm I hit my anchor).