You've been magically transported to Faerûn and get a choice

Either you stay in your regular human form, or you get to pick a class but are infected with a tadpole.

You retain all of your game knowledge about the realm, except for how the story goes. You can spawn yourself anywhere you like but chronologically you are at the point where Tav starts on the Ravaged Beach. There are no obvious ways back to the real world.

EDIT for clarity: You're completely unaware of how to get back to the real world at first, or if you ever will. But since this is a world of magic, you do know that there are Wish spells and portals that could offer salvation, if you should want it. In short: there may be a way back for you, but very difficult/near impossible to find.

What do you choose, and what do you do after?

I would Absolutely become a Bard and join Tav's party, but chill at their camp to take care of Scratch while they go out doing the dangerous stuff. I'd give advice to make sure they end up getting rid of our tadpoles, hug Karlach at every opportunity, provide emotional support to Astarion, gossip with Shadowheart about Lae'zel and the others while checking out Halsin together, organize their camp supplies, maintain the tents and make the food.

So why pick a bard, you ask? Every morning after the quadruple "ahhh" they'd be greeted by a wonderful breakfast down down down by the river, accompanied by me singing over the violin I can play now. I'll give them their buffs in the morning and occasionally step out of camp if they need a quick Feather Fall spell, to do their shopping for them or to play in a tavern for a while to earn some extra gold.

That's right. I'd essentially be nothing more than a magical housewife to the heroes in this fantastical realm of magic and wonder. No regrets.