40 miles is a fairly good shakeout for a new bike.
1- I agree with sloar on the minor scratches. They look bad now, but wait a while, the bike will eventually look badass.
2- No gasoline. Use your chainlube to clean the chain. you can also lightly lubricate the other moving parts. Keep oil off the brake pads/rims.
3- Keep the bike reasonably free of muck. Debris on the rims will hurt your braking. Make sure the pads are contacting the rims well.
4- Sounds like your derailleur cables may have stretched a bit. This is normal. You'll need to use the cable adjusters. Learn how here.