I just started bowling a curve but I'm still having some problems?

Okay so I just discovered I could bowl a curve last time I went bowling with my mom and dad. I bowl a curve where I don't put my thumb in the thumb hole. When I throw the ball I basically just twist my wrist. First of all, I'd like to point out that i start out with my right foot on the middle dot. Okay so usually what happens is the ball starts going out diagonally across the lane towards the right side of the lane. Then it starts to curve, and of course goes to the left. Now the problem there is that most of the time it curves too much and goes far past the brooklyn, resulting in to strike . How can I fix that? My dad said that I need to throw it down the lane faster, but i find that very difficult when im not gripping the ball in the thumb hole, because if i go faster i'm going to drop the ball. Also what sometimes happens it sometimes it doesn't go diagonally down the lane, it goes straight, and curves right into the gutter. My dad says this is because i'm trying too hard and I just need to let it flow naturally, but this is also hard for me because I want to get this right and I feel like I need to try my hardest. So does anyone have any solutions to both these problems so that i land in the pocket almost every time? I'm 13 years old if that means anything