There's some bad info in this thread, so before I get to the spin stuff, I'm going to clear some things up.
1) It's not about getting more air to spin more
Spin is not about getting more air, it's about getting more power into your rotation.
Yes as you move to bigger rotations, you'll need more air, but that doesn't happen until you start doing much bigger tricks. For 180s, 360s and even 540s, you barely need any airtime. The whole 'get more air to spin more' is bad advice and it means you're setting up your spin the wrong way.
2) Don't pop harder to spin more
The purpose of pop is not to get more air and spin more, it's to set you up for a stable air. To spin more you add power to your carve, not power to your pop.
You want a firm, good pop, but you absolutely do not need to pop harder to spin bigger spins.
Okay now that I've covered that, on to the spinning.
1) To fix that 180
I'm not sure if you wanted advice to fix the 180 as well, but just in case you did, you were mainly messing up that 180 because you didn't end it in a blind landing.
You can see at the end of that rotation that your head continues to look forward at the end of the rotation. That's why you're over-rotating into a 270 instead of ending at 180. With backside 180s you have to end the spin by looking back at the knuckle, otherwise you'll over-rotate like you did in the video.
2) To take this to 360s
It's all about your carve line. Right now you're not carving into the jump, you're coming in on an edge while mostly riding straight, which is fine for 180s since they require barely any rotation.
However, for 360s and beyond you want to start using proper carving. This means entering the jump at an angle and carving up the take-off to create spin power. The more spin you need, the harder you set up and release that carve.
I've attached a rough diagram of what your carve line should look like coming into the jump.
If you want more in-depth info on the carve line, I have an old blog I did on the subject awhile back here:
The Secret To An Effortless 360 Rotation - The Perfect Carve Line
One last thing, besides the carve line as already mentioned, you want to quiet down that upper body and start relying more on having your upper body lead that rotation, while getting power for the carve to power the spin (instead of throwing your hands around).
Think of it like this:
Body rotation = starts and leads the spin and tells your body where to spin
Carve = creates power to spin
Pop = releases your spin power and sets you up for stable air
If done right, your upper body will lead the spin, the carve and pop will create power and release it into the spin, and your lower body will follow your upper body around into the spin.
ps - in the image below, the swap edge point simply means it's where you go from your setup carve to your final carve. So for example, if you were doing a backside 360, that swap edge point is where you're going from heelside to engaging your toeside edge and carving up the jump.