Good advice on throttle and props so far. If you can't kill the idle thrust, then it will be a problem on approach. One way to tell is: will the plane sit still at idle on pavement or does it start rolling as soon as you let it go? If you can't cut it back to a sitting idle, it's too much.

If the motor won't idle down without dying, the idle mixture needs to be adjusted. It's probably too rich. See if it speeds up when you pinch the fuel line at idle throttle. If it speeds up and stays running for a few seconds after pinching the fuel line shut, you could lean out the idle mixture. That will allow you to slow the idle another click or two.

Also, when the plane is on approach, are you aiming for the end of the runway, or right in front of yourself. You need to have the plane on a glideslope towards the end of the runway. If you are aiming for the spot in front of you, half the runway is gone before you even had a chance. Then when you flare out the plane carries even farther, pretty soon you are out of runway. I know this is a problem I had many years ago. Adjust your pattern down the runway.

You could also just need a little more up trim. There's no guarantee the landing trim will be the same as flying trim. You could retrim manually. Or you could put a slight adjustment mixed on a switch.