No education is ever wasted, but sometimes test fees are. The fact that you are still thinking about engineering means you should probably take the AP tests and wait and see where you apply and where you get in.
If you forgot to mention that you have an acceptance from RISD, never mind.
All schools have their own AP credit acceptance policies. Some offer more, some offer less credit. Schools that offer less credit are generally more prestigious and feel their own courses are much better than anything you could have done in high school. (They are right about this, for most high schools,)
Early in high school, when you don’t know for sure where you are going, it makes sense to take the AP tests. By May of senior year, when you have your acceptances in hand, you may want to skip those that you know you won’t get credit for. Your dream school may not offer credit, but the school you get accepted to with good financial aid may.