Hi Steven, welcome to the site.
If you could post a video of yourself bowling from the side and from behind I might be able to see if you can do something to improve your physical game.
First here are some check points that will help you improve:
1. Hold your balance until the ball hits the pins
2. Watch the ball all the way through the pins
3. Develop a feel for where on the lane you want the ball to hook (break point).
4. Watch the ball reaction and break point of other bowlers who are doing well and try to get your ball to hook back to the pocket from the same area. If you are a power player and the straighter players are doing well playing up the 5 board and hooking the ball to the pocket at 45ft from the 5 all you need to do is figure out where you need to stand and aim to get the ball to the 5 board at 45ft. If you are a straighter player and the power players are crossing the 20 board at the arrows and the ball is going out to the 5 board at 45ft then you just need to figure how to get your ball to react from the same point by choosing the right ball and standing on the right board, aim at the right board and use the right amount of side rotation and speed to get your ball to do the same. Don't just keep grinding in the same shot over and over and expect different results because it will not happen.
5. After doing #1 and #2 check your slide foot to see if it is on the same board every time and that you aren't drifting. Drifting = finishing in a different spot every shot, not finishing on a different board than you started.
6. Keep your release smooth, grabbing the ball at the release is never a good thing.
To work on your mental game you must first understand what the mental game is. The mental game is not just staying focused and concentrating and deep breathing, all of those things help, but they all go away as soon as you don't know what to do. Frustration leads to a downward spiral, the worse you do the more frustrated you become and the more frustrated you become, the worse you do.
You must figure out why you are leaving all of those 10 pins, or why your ball goes high on the head pin one shot, then washes out after you make adjustments for the ball going high.
All of these frustration points are questions and the lack of answers cause the frustration to grow. What specifically is causing your frustrations can be answered and then you develop your skills to deal
with it so the next time it happens you will know the proper adjustment and it will not kill your entire outing.