I think I may have messed up getting Sylva

[Archerodees]

Not exactly sure what happened, first time playing, but I didn't even know about the snails. I got a terrarium reward, I think, so I set it up, put soil and zinc and the horn and played the horn. (I was literally just following the quest instructions) Then a small cutscene played and the snail appeared. Then went through the emotes one-by-one until I found the one it liked, but then it just disappeared.

So now on the terrarium it says it needs to be near the snail but the first time it wasn't, how could I know. So have I messed up or will there be another chance?

[PhailRaptor]

You just need to grab the Terrarium, and run over to where she moved after you did the correct emote. Place it next to her and you'll be given the option to Befriend her, and she'll go into the Terrarium.

Like most things in this game, it's explained very, very poorly.

[Archerodees]

Edit - nvm, you were right, it moved some distance away, had an icon above it. Got it now, cheers.