Press flag twice so there aren't any bugs, especially when you're on the lose screen. A to go left, D to go right, spacebar to jump. Don't touch the bottom. If you want a slightly harder level, press 2. The easier level will pop up when you press the flag.
This took me like 3 hours total, the hardest part was just getting the scrolling to go smoothly. The actual level just repeats itself, and this was more of a "I'm bored" project, but I think it could become pretty cool.