Left = hmm, not quite, Right = looks interesting, Right = this person too, Left = don't think so... – whoops, that person was actually quite cool!
Was your thumb a little too fast? Don't fret, as a Premium member you can undo an unlimited number of swipes.
However, you can only undo the last swipe, i.e. go back to the last profile you saw.
How to undo a swipe:
Whether it's a like or a swipe to the left, you can always undo decisions with the circular arrow symbol at the top right. With a single click, you can view the previous profile again and give them a second glance.