Hi
@Keeley, you're posting in exactly the right place - POTV! We're glad to have you here and you won't find anywhere more welcoming than this. It's nice to meet you.
As for your question, don't worry about it, you won't damage your tank.
When I started vaping a little over a year ago I was putting 80/20 in a little cig-a-like and it did no harm, it didn't even gum up the coil. Even if it does, it's not like they're expensive just put another one in and forget about it. I still often over eagerly wreck the first coil of a devices in my even now.
It's probably just as cheap to replace a coil as to use a nic-shot anyway.
If you do go down the buying pure PG & VG route, who knows, we might even make a mixologist out of you!
Happy vaping and welcome to POTV.
Hugz, peace and blessings.