I wish I could tell you but I don't know how Canapple tipping/economy works. In the US a 15% tip in normal. I always over tip if they do a good job or are friendly. Since waitresses here don't have a minimum wage. But normally for all good service I over tip. If you remember her reaction it might hint at it. Generally a little bigger smile or something means good tip. But I dunno man google it
---------- Post added at 09:21 AM ---------- Previous post was at 09:13 AM ----------
As I think you're drunk and I have to much free time I looked it up. It said 15% is normal there as well. Now assuming I read this correctly you got 20 dollars off which means the actual bill was $23.33 so tipping 3 dollar is a roughly 13% tip of that.
Long story short.
You under tipped by 2% or about $.5 of the normal 15% however tipping isn't a exact law so it's nice you gave her something. (But honestly if she was wearing a low cut shirt she was probably aiming to make better tips)