The inflation you're mentioning is the real risk you're running by keeping your money in pesos, so you're already losing even if you don't see it day by day. What changes with index funds is that the risk is more visible - you see fluctuations on the screen - but in exchange you get exposure to companies that generate real value, not just currency erosion.
Where a lot of people mess up is thinking that six months is enough time to put it all in at once. If you're really scared of losing, put it in tranches over the next few months or years; that way you dilute the risk of jumping in right before a crash. And another thing: check carefully what fund you're buying, because management costs (annual fees) can eat up a decent chunk of your gains if they're too high.