Given that it’s obviously heavily mixed with CA blood I highly doubt you’ll end up with a large boa, it just may not stay on the true dwarf end of the size spectrum.
You can try to strum the tail and feel for hemipenes. Just pinch it from the top and bottom and run your fingers down towards the tail tip. About an inch or so past it’s vent you’ll feel bumps if it’s a male.
It’s unlikely Nirvana will get anywhere near 8-9’, given the likely Nicaraguan ancestry (at least in part), and most boas don’t tend to get that big. Some can, but most don’t.
If you want, you can try running your fingers from the vent to the tail with a little gentle pressure. If you feel discernable bumps, those are likely the hemipenes and you have a male. If you don’t feel anything, you likely have a female. That’s probably the least invasive way to sex a snake.
Edit: @ballornothing beat me to it. 
Oh right, I guess I’ll find out in a few years, and by then I’ll be so accustomed to them that even they do find themselves on the longer side of things, they won’t seem that big too me XD
I might give that a go, thanks both they don’t seem to like anything touching their tail tho, or their head, i need to acclimatise them to that, slowly though. I’m still a little nervous when i handle them, but we seem to be getting more comfortable with each other.
Is it just two lumps like male mammals?
It’ll be less likely to startle them if you just sort of let them slither through your hands, and then just apply a bit of gentle pressure when your hands start to get near the vent to feel for the hemipenes. My blood python is a bit touchy about her tail, but she doesn’t seem bothered if I touch her tail as she slides through my hands. I think some snakes get startled if their tail is suddenly grabbed or touched because it probably feels predatory to them, but if they’re sliding through your hands, then they’re expecting that contact and know what it is, so it’s not so concerning to them.
All my snakes are female, so I don’t actually have any first-hand experience with feeling hemipenes. But I’ve heard that they sort of feel like two little speed bumps. 
I will think of your comparison the next time I go over a speed bump 
Haha speedbumps! I’ll give it a go next time i handle them, they’ve just eaten yesterday so I’ll give them a few days.
Temps today after lowering the stat are giving me 73 cool 80 warm, and 82 hotspot so I’ve bumped it up slightly, will check the temps again this evening.
I did notice that when the uvb turns off that does create a 2-3 degree drop in the cool end.
ya I own a CA and that definatly looks like one
this is some generic BCI with random genes/hets, its a mix and unable to get any clear indicator, could even have some BCC in its lineage further back.