I assume you play on a PC.
There are different cases where this "facing away" may occur.
1) The aiming marker is still on the flag but the avatar has turned, appearing like a lefthander.
In this case, the putt will work !to the right direction! regardless, and if you slightly move the marker, the avatar will turn around.
2) you see no aiming marker at the flag or elsewhere before you.
Then, you (or Sasquash) have moved the marker and the putt would hit to whereever it is. To find it, select the reverse view or use the mini map. Once you have positioned it behind the flag, you should be able to re-position it to your liking.
User's workarounds:
- in a solo round, save the game and return right away. Then, the set-up will (hopefully) be corrected.
- or, initiate a mini putt, low power, hit it far off the ding. You will lose a stroke but "win" a new set-up for the next putt.