I guess the “game” starts as soon as your code kicks in. But maybe you can come up with something else than a 2nd button. For example make a bar fill as long as the button is pressed and once it is full it selects the level. So in short: use the short button press for one action and long button press for an other.
Yeah, I have the same problem, where adding a reset button would be good. However try working around it. Having to reset is not a fun game mechanic. Maybe you can find a way the player can fix his mistakes and have an other try without reset? If this doesn’t work but getting killed resets the game, try to place instant kill obstacles (like spikes or such) in the parts of the level where the player might need a reset. Or maybe even reset buttons the player can activate in game by standing on them or something…