Visick, I don't think you MUST skip a letter you already have.
Correct.
Rule 9a:
9a - In the event you come to a letter than you already have, you may skip that letter w/o penalty (w/o using one of your 3 free skips) to go to the next available letter. You may only use this to move to 1 letter down the road - only 1 LETTER SKIP per turn. All other rules above apply.