Put it this way. Training isn't cheap so they may not like that you "resigned". Plus other airlines will be very hesitant to invest $20K into you because you left another during training. I think your safe bet would to not mention that you left. Why would you quit because you weren't flying the sim good? Like Saab said "Only leave when they kick you out"

I hate being negative but once you get to the sims they've invested a lot of money at this point so it's going to hurt you in the future.