Dear Couragious Gryffindor,
House affiliation has no bearing on areas of magical talent. It is possible to achieve even Master-level competency in any subject, be it Herbology, Potions, Tranfiguration, Charms, or other areas of the curriculum, whether ones House is Gryffindor, Hufflepuff, Ravenclaw, or Slytherin.
As to whether the Sorting Hat has ever been wrong, Professor Dumbledore occasionally expressed the opinion that sometimes we Sort too soon. However, never fear. You are as you sign yourself, a true Gryffindor. If you question this, I encourage you to look within to find your true courage and loyalty.
Head, Gryffindor House
Hogwarts School of Witchcraft and Wizardry