Five days, with one day left for you
A longer stay is a chance to do less rushing, not a reason to add five attractions a day. This plan gives you beach time, two wildlife stops and Port Isabel history. Day four is deliberately open for the activity your group chooses; day five returns to the beach instead of sending you somewhere new just to fill the list.
Days one and two: the Gulf and wildlife
Start at Isla Blanca Park once you're settled. On the next suitable day, visit the Birding Center and, if everyone wants a second stop, Sea Turtle, Inc.. Check opening arrangements and leave a break between visits.
Day three: Port Isabel
Visit the lighthouse and ask about current hours at the Historical Museum. If the tower climb doesn't suit your group, don't make the whole day depend on it. Explore Port Isabel and choose a meal or another activity instead.
Day four: add the booking you chose
Use this day for a fishing charter, dolphin-watching outing, a lesson or simply a day at your accommodation. Book directly with the provider, then enter the meeting point, time and cancellation details in My Trip. No generic tour is automatically added as if you had booked it.
Day five: go back, or change the plan
The saved suggestion returns to Isla Blanca, on a different day from your first visit. If you'd prefer another beach, swap it for Andy Bowie or a convenient city access. If this is departure day, keep it short.
The open day also gives you somewhere to move a weather-dependent booking. Check ocean conditions and the provider's advice; an empty day is useful, but it doesn't guarantee another sailing or reservation will be available.