The scientific case for electrolyte depletion as a general cause of cramps in exercise is extremely weak. That said, some people seem to cramp for idiosyncratic reasons and you might find that electrolytes seem to work for you. Whether it's actually the electrolytes or other changes to habits that do the trick, it's hard to know, but there's not really any harm in trying (other than to your wallet).
To get down to the basic reality of cramps, 99% of the time, they are due to fitness or fatigue issues. Feeling like you have gas in the tank (i.e. that you've still got plenty of glycogen stores) doesn't mean your muscles aren't fatigued from, say, a long ride in the car to get to your race, or insufficient rest leading up to the event, or something like that. I'm familiar with the feeling you describe, of feeling snappy but getting cramps nonetheless. Despite feeling like you can still go, it really is just another way of your body telling you that it's out of gas. I've been there, and it is frustrating, but it also beats having heavy legs the whole race. In my experience, cramps are often how fatigue manifests for me after making lots of hard efforts. Keep building fitness and endurance, and do everything you can to optimize your preparation for an event, and you should cramp less often. But sometimes it happens. If it happens and you still get 6th, that's not too bad an outcome.