Trouble getting down is often a result of a few factors. One would be the idle speed of the engine and the pitch of the prop.

First, see if your engine will run at lower idle speed. If not, you might need to give some attention to tuning the low speed mixture. At idle, you pinch the fuel line for 3-5 seconds. If the engine speeds up appreciably, you can lean out the low speed needle. That will make it run faster, but only until you change the idle setting of your throttle. Once you adjust it lower, the motor will be capable of running slower, giving you steeper approaches.

Also, you might try switching to a lower pitch, larger diameter prop. This type of prop will give you more static thrust at full throttle - and less thrust/more drag at idle. That will also help make your approaches steeper.