Well since your saying you can only going half way…. maybe its the your leaning back before you jump and spin. You might also not be spinning hard enough/not jumping high enough. Practice on flats, stay balanced, commit.imo
are you turning your shoulders or your hips?i find that if i only turn my hips i land 90 all day.if im going to do a 180, or any spin, i first wind up my shoulders as far as i can into my spindirection, then turn my head the same way as i pop. as the motionbecomes more fluid it becomes harder (for me) to 180 than to go 3. also i learned flat instead of putting in an ollie. i wound up and just spun180 riding flat, letting my shoulders wind up for the spin and my hips to execute.
For frontsides (turning your front to downhill first), try to match your shoulders up to the direction you are going while airborne, then bring your board around to match before landing.For backsides (turning your back to downhill first), some people find them easier to actually land while looking uphill. I'm not BSing, try it it might work for you.