A week ago I bought a one drop Top Deck along with some strings and their standard flow groove pads. However, I just realized that Top Deck uses the " slim " 19mm flow groove not the standard one.
So I’m afraid it won’t fit properly or have snagging problems. Is it that big of a deal or I should be fine?
They’re significantly thicker so they’ll probably stick out of the response groove a decent amount. I wouldn’t recommend using them in the wrong yo-yo.
Unfortunately I wasn’t aware of this, i already ordered them a week ago so i won’t own the slim ones that are recommended, so i was wondering if anyone experienced this…
If they stick out the yoyo will probably be responsive then, I don’t use thick strings but dont think that will help. ( unlucky 
)
On the plus side, since you just ordered the yo-yo the pads shouldn’t need to be replaced any time soon. And it looks like you ordered a pair of YYF 19mm slim pads that will fit the Top Deck as well.
I would offer to send you replacements, but the shipping cost wouldn’t really be worth it for international shipping. But… what I can do… The next time you place an order just make a note mentioning this and I’ll throw in a free pair for you. 
Well i really appreciate your concern, the YYF pads are actually for another yoyo that i currently own 
It’s okay i might use flowable silicone or something…