The Titanic sunk 90 years ago and with it the kind of "dress code" you are worrying about. Sweats are fine, jeans are fine, shorts are fine during the day and while lounging and walking around the ship and ports.
Dress "codes" if there really is such a thing applies to suggested attire for the dining room for the evening meal. Your cruise documents, daily announcements will describe suggested attire for casual, semi formal and formal evening attire.
Relax and enjoy your Alaska cruise.
I'd be happy to have you sit next to me wearing the outfit you describe.