Obviously this is an issue with the board (as long as your not lying about your abilities on your t-rice). However, this board just needs different inputs on the approach and takeoff to give you desired maneuver and landing... To give you a better idea what this board likes, i would do some toe-toe 180's. This is best done on green/blue groomers. Carve toeside, at the completion of the turn, takeoff your toeside edge, do a frontside 180, and land on your toeside edge going switch (this will now be your downhill edge), and ride a switch toeside carve to completion and another frontside 180 landing on your toes regular and repeat. This will give you an idea what the board needs for input, you will also get many many more tries in one run than park laps, and also with less consequence.
I personally do not recommend spinning off a flat base, it increases the chance of prespin (and edge catch) and doesn't offer the same control that spinning of an engaged edge does. Also you can spin backside off your heels or toes, just keep that in mind.
This next part may or may not be too simple for you, but just so i know we are on the same page:
-On the run in be on either edge or flatbase, with knees bent, prewind if necessary (depends on desired spin vs jump size)
-Take off an engaged edge (i prefer toeside)
-At takeoff pop off of both feet evenly (rather than ollie or nollie), till you feel better on this board at least
-just prior to takeoff start unloading your prewind so that at takeoff you have your upper body very slightly more in the direction of the spin than your lower body (your lower body still going straight at this point)
-immediately after takeoff suck your legs up (grab if desired), continue moving your upper body in direction of spin, tighten your core to transfer this upper body energy to your board, also add in a scissoring of the feet motion to speed up the spin.
-spot landing and either open up to slow down spin, or try to get into an even smaller ball to speed up spin
One last note, to make for the smoothest landing on backside 540's land looking back at the lip, or at the knuckle... Trying to look in the direction of travel while landing a spin where the last 180 is backside is uncomfortable at best, and risking washing out or over-rotating
Good luck and have fun, i really think the toe-toe 180's will allow you to teach yourself what the board wants in one run, plus its really fun