G'day Mate,
Ask your instructor, he should be able to help.
If not, do this: run engine up to full speed, on the ground, to get it hot, then take it to idle, stand behind engine, & squeeze off the fuel line to the carby with your thumb & forefinger, beware of the PROP, it will cut you, listen to the engine, if it speeds up a lot, before slowing down & stopping, it is too RICH, lean the idle mixture 1/8th of a turn, this is where the instructor will help.
If it just dies without speeding up it is too lean, richen mixture.
You need it to speed up a small amount, maybe 50 revs or so, before it dies, then it is perfect.
Your high speed mixture should be rich enough so that at full power, when the nose of the plane is held up at about 90 degrees, it should pick up some revs, if it doesn't or it dies, it is too LEAN, richen high speed needle, until it does.
Then the mixtures are set, leave them alone after that. The biggest problem I see at flying fields is when people continually tweak their needle valves, & have no idea what a properly tuned engine should sound like.
A couple of weeks ago a new flyer turned up at our field, he said he tuned his engine to perfection, he is a retired car mechanic, when we got it running, it was 1/2 turn too lean, that is a lot in our engines, it was retuned & has not had to touch it since.