It is common to allow the string as you come to full draw to let the string push your finger down onto the arrow. This is also a common cause of the arrow falling off the shelf.
Try, when you first hook the string to set your index finger about 1/8th inch above the nock (just not quite touching it) and try to resist letting the string push your finger down. Many find that a "spacer" on the tab helps hold the finger off the nock. I do not know how long your Sage is but this is made worse with shorter bows.
Also, if you can, have someone check your elbow height at full draw. Getting you string elbow too high can also do this. If you are just starting it may be both.