Playing on Nats is nothing but a waste of cash. There's much better betting opportunities on board then betting on Nats.
Since visitors are a poor road team and they won 1 game already, I don't see any reason to bet on them.
What about betting on Cubs?
There's good way to deal with heavy juice lines like this. Don't place your wagers "to win", use "Risk". I mean, don't use American Odds! Place your wagers in a Decimal Odds approach. Odds for Cubs are -286 (Not -310 in Matchbook) and you should not place 286$, just place 100$ to win 35-38$. Even if you lose, you won't lose too much btw.