I'd go about it slightly differently.
Don’t worry about the AI at all, use the real horizon.
The only instrument to use is the altimeter. Make sure you know the height at which you enter the turn.
I think a problem stems form people over using the instruments - after all this is a visual manoeuver and getting use to doing it with reference to the horizon alone is helpful.
You will probably find at first you don’t get to 45 degrees because you feel it is to steep. Don’t worry, your instructor will soon tell you.
Once you are in the turn keep the horizon in the same place, flicking your eyes down very occasionally to check you are maintaining exactly the same height.
Look for the buffet as you enter your prop wash - if you don’t get it, you are not doing in right.
Works every time!