It's already been pointed out that the primaries are not equal in intensity and that primary turn out isn't actually indicative of general election turnout.
I'm not worried anyway. The Republicans are so fractured it seems unlikely they'll be able to put things back together, especially behind the most likely candidate. It's going to take everything they have to just keep the party from imploding. You've got Republican mega financiers saying they'll spend anything to defeat Trump, Republican party members suggesting they'll vote outside the party if Trump is the candidate, and all sorts of chatter about third party runs, etc. That's a lot of worms to try and cram back in by November. And if the candidate is Trump, the Republicans get a guy who can't be controlled, who's largely gone unvetted by the Republicans, and the Democratic oppo research team is going to hit him like a Mack truck. Granted, there's plenty of material in the other direction, but it's presumably stuff we've been bored about for ages.