could literally be how the dream was planned out to be and you doing reality checks and realising you are lucid could be part of the dream itself, already programmed, not you realising on the spot
Planned out by whom, exactly? You're suggesting a form of predestination within natural constructs created by our own minds.

However, is this what a lucid dream really is? Just you getting it into your mind that you will do these 'reality checks' or go lucid, so you just dream about it and experience this?
Ah, but if you can't trust your own experience, what can you trust? If you experience a lucid dream, then by definition you know that you're dreaming. How can you dream that you know that you're dreaming without knowing that you're dreaming?

I might do them as part of my dream without making a conscious descision to do it
That's the point of RCs, you know. You do them during the day so you do them automatically while you're dreaming. You might not be lucid while you're doing the RC; the point of the RC is to provide clues that you're dreaming. (ie: Hey, I'm not supposed to have seven fingers. I must be dreaming.)

without making a conscious descision to do it and then in my dream, which is already planned out and I have no control over
Again, planned out by whom? Dreams are mutable; they change according to what your mind is focused on at any given moment. If you suddenly become transfixed by the dolphins swimming along through the air, you might forget all about the zombies that were chasing you a moment ago. Dreams aren't planned out; they change too quickly.

but not really realise that I am dreaming, and then wake up thinking I was lucid.
Then you aren't really lucid. Lucidity, basically, is defined as being aware that you're dreaming. Some would argue that there are different levels of lucidity, but you can exert some form of control over your environment without being fully lucid. As you have more lucid dreams, you start to be able to tell just how lucid you really were.

There's a bunch of different posts here speculating on the various "levels" of lucidity.