A rollercoaster only takes a minute, so even if they should make you drop or rise, you'll have plenty of time to react to that after the ride!
Just keep scanning away all day on your Libre to see what happens, and at the end of the day you'll have learnt stuff about your diabetes you didn't know before.
I've been to an amusement park a while back, and while I did notice a significant effect from the more scary rollercoasters, the unusual activity (you tend to walk a lot in those parks) plus the unusual food had a much bigger impact.
I'd try to look at it as an experiment to learn from, very useful.
Rolloercoaster could make you rise or drop, no way to predict without trying.
They could make you rise because the adrenalin can cause your liver to dump some extra glucose in your bloodstream.
The too scary rollercoaster I went in made me drop like a stone, I suppose that being terrified is very hard work and uses up a lot of glucose. It wasn't a problem: I spotted the drop on my Libre before I dropped into hypo territory and had a small bite to nudge it up a little.
Take a fingerprick meter and teststrips with you as well, Libre can be a bit slow to recognise fast changes in BG, or it can even decide your BG changes too fast for it to give a trustworthy result and it will tell you to scan again in 10 minutes.
And of course bring stuff to treat or prevent a hypo with.
But the most important thing is: enjoy!