That is not good - you will have put the wrong polarity of voltage on the electrolytic capacitor. Fortunately, the current is limited, so it’s not likely to have done much harm. Had the resistors not been there, it would have overloaded your Arduino output, and the capacitor could possibly have exploded.
If you buy an emonTx Shield, emonTx or emonPi and need to change the burden resistor, you’ll need to use a ¼ W or 0.3 W, because there won’t be room for anything larger.