OUCH- Even though it's hard to see on white, try using a LOT less SG. A nickel size amount sounds like an awful lot to me and I use SG on a minivan (big panels). When I apply it (usually using a yellow foam " hand waxing" pad), I just put the pad over the hole in the bottle's spout and shake the bottle. This deposits a VERY small spot of SG on the pad. Then I move the pad and do it again and repeat a few times. I end up with small dots of SG on the applicator, enough for at least half a panel, maybe even a whole one depending on the vehicle. It's pretty amazing how little SG is really needed.
For complete/even coverage on light colored vehicles, it's very important to use a consistent method so you're always doing the same thing- it's easy to get into habits, so get into GOOD ones. I work off contour lines and panel breaks on the vehicle and go over each section more than once to make sure I don't miss an area.
As you work around the vehicle, your pad will probably get more and more saturated with SG, so watch that you don't end up using too much on the panels you do last. To help you see the SG during removal, fog the surface with your breath and remove with a consistent method (like what you did when applying).