Remember too that they may have been chilled from the ride home, and this is all new to them. Chicks huddle for security as much as for warmth. Our mission, should we choose to accept it, is to figure out the difference. <sigh> Not always an easy task.
If your brooder is in the house, the highest setting might actually end up being too warm. I know, they're huddling in the lowest corner, but if you can take @Fire Ant Farm photo to heart, I'd try to even out the pad so the height difference from front to back isn't too steep and most of the pad is at back level. I don't know (or remember) what pad you have but if it's the one with the digital control, for inside the house 5 should be fine. I'd worry about them getting too deep into a corner and the front ones keeping the back ones from getting out to cool off. You've got this! The learning curve isn't as sharp as with a heat lamp - always lowering and raising it and no place for chicks to cool off - so do what you know makes common sense....small adjustments the first day or so aren't unusual no matter what you use for brooding. By the end of today, I'll wager you have energetic chicks who have figured out exactly where they are and where "mom" is and you'll be sitting with your feet up sipping glass of wine!