On mobile, forms have the same padding as on desktop. This wasn't an issue for me some time ago but when a user opened my form they showed me that on their iphone the choice for a question could not fit more than a single word on a single line (for my phone which is a large screen, I can at least get 2 words on a line for a choice selection).
I noticed that Smartsheet has increased the padding so that it takes about half the screen real estate from the padding on both the left and right. This fixed pixel padding looks fine on desktop but there doesn't appear to be any testing on mobile before implementing huge changes like this.
I recommend setting a separate padding for smaller screens/devices.
PS: This also applies to small size embeds as it's just not responsive to provide any padding reduction on smaller width displays of the form.