hero.gold is the actual amount of gold your hero has at the moment, so it is 100% bulletproof for this level.
On the other hand, manually counting the gold you’ve collected can result in issues when you are walking towards a coin and your hero unexpectedly collects another coin that just spawned in the way, or when two coins spawn too close to each other and your hero collects both counting as just one. This is why I suggested resubmitting, every time you press “Submit” (not “run”) you get a new random seed and your game plays differently.
Did you manage to beat the level? If not, please post your updated code so I could try it here as well.