Just a little update to the problem of leaning on the throttle while trying to brake. I learned a nifty trick that might help. I like to keep my wrist bent upwards at a slight angle while I hold the throttle.
This allows for two things. One, since my wrist is closer to the end of my range of motion, I can’t physically twist the throttle wide open, which helps control my speed. Two, the act of reaching for the front brake automatically rolls the throttle closed.
It might feel a little awkward to hold your wrist like that, but its nice security when you’re learning how to ride. Like others have commented, you want a smooth roll-off of the throttle while smoothly applying the brake.