You don't want to let your fears get the best of you. Trust me, you don't. If you have never been on it before, I suggest you give a try. If you don't like it after you have tried it, let your dad know and he should understand for future times.
The Tower of Terror is a very fun ride. I rode it years ago before they changed the drop sequence. I was about 8 years old then and I did't want to go on. I cried and shook like a leaf lol. I am very glad I tried it! Because the scenery is very realistic, it can be scary...due to the nerving anticipation. Once you are on the ride and once you exit, you will say to yourself, "WOW"! Many many people fear this ride, yet many many people LOVE it. Sometimes it is what you fear that is the most fun.
This reminds me of a time when I went to 6 Flags. I didn't want to ride Superman...and once I got there and saw it, I told my dad I was not going on. (This was last summer and only he and I went). I have a fear of heights and looking at that thing solidified my "no" lol. He didn't hold back for me, and kept moving right until he sat in the car. I had no choice but go on. I was shaking so hard, complete strangers asked if I was okay lol. Once the ride was over, I was EXTREMELY glad I went on. It was a blast! (sure, I had my eyes closed going up that first big drop) but talk about air time! My dad forced me (kindly) onto every other ride that I refused to go on and I loved each one more and more. Anyway, the point of this anecdote is to show you that you can not be too certain about things unless you fight your fear and try something at least once.
Since you haven't been on the Tower of Terror, you don't know for certain how scary it is. Just try not and think about fear as you walk through the lobby and boiler room. And remember, it is Disney...everything is safe, fun and enjoyable! The magic is always on your side!!
I say go for it and show your dad how brave you are! I can almost promise you, you will love the ride! Go and experience some good ol' Disney magic!