I used the trinewbies 18-week intermediate sprint program last year - my first season of triathlon - and successfully completed 2 sprints. Though the training time was very long IMHO (I felt ready after 12 weeks), I was definitely prepared to complete the race. As a complete beginner, being able to follow the program and get the workouts in gave me the confidence that I could successfully do the distance.

Like the other posters said, you already seem to have a decent base for the sprint distance. If you're looking for a challenge, you might try doing 10 weeks of the intermediate program (first 8 weeks and then a taper) if the beginner's program seems too easy.

In any case, enjoy yourself!