Remember, this is still a hyper young pup. At 5 months old they'll have "brainfarts" (my dad introduced me to that phrase :roll: ) and forget how to mind. IMO, you need to get more leash control on this dog. Don't allow him to surge ahead while tracking. Also, you may have not done enough scent pad work, like you said, for him to be more careful.
I train young dogs and puppies to track by doing exactly what you are doing: place a tiny amount of food in each footstep. I also make sure the dog is extremely hungry, so then they'll want every single piece of the food (usually beef liver or freeze-dried chicken treats) and won't skip it over. I also make sure, however, to lay a scent pad at the beginning and at the end. At the very first trainings, all I teach the dog is to smell the scent pad and to recognize that "Seek" (or whatever command you choose to use) means, "Get that nose down and sniff to find some good stuff!" I put treats all over the scent pad, then gradually reduce them to be triangular in shape. Make sure you introduce tracking flags from the beginning, because the dog will learn that to the right of the flag will be the track and therefore rewards!
After teaching the dog to begin taking scent at the scent pad, I will start the footstep baited tracking. To get the dog's interest spiked, I will crate the dog in hearing range, and call to him and tease him, so he WANTS to track and get the prize at the end. I make sure I always have someone else with me to get the harness on and untangle my tracking line before I head back to the dog. Therefore we can start immediately on the track, instead of frustrating the dog by spending time hooking him up, etc. Any sort of delay at the start can quickly kill that enthusiasm I kicked up with the calling and teasing. I also point out every single footstep treat, so the dog learns to work carefully. As soon as the dog starts to get it, I stop pointing out the bait and I let the dog do it himself. I usually keep a very short leash on them at this point, 2-3 ft at the most. At the end of the track, the dog always finds a whole bunch of food, and also it's favorite toy. Then, we engage in play for a few minutes to reinforce the idea that when they reach the end of the track there is a fun and rewarding experience!
After the dog has been doing this for a few weeks (depending on the time spent every week) I VERY slowly begin reducing the bait. This way the dog still scents out every footstep. Once you start reducing the bait, you'll need to introduce the articles. These need to be hand size or smaller, as well as a variety of fabrics and materials. I like leather gloves or simply squares and cloth scraps. At a few trials I've been at, all the articles have been were squares of leather and/or cloth. Also, make sure the material used is the same darkness or lightness of the surrounding grasses. We want the dog to scent the article out, not just rush forward because they see it!
I could practically write a book here about teaching tracking, but I'll leave you with this: I would recommend you review the requirements for SchH tracking and train to meet them. I, personally, like to over-train a dog, such as train to a SchH2 level before trying for a SchH1. It won't hurt anything, it may take a little longer, but the stress of the trial (which you WILL have) won't affect the dog as badly as if he was only trained for the SchH1 level. Go to a very good trainer or SchH club with very experienced members that can assist you in tracklaying techniques and training. Remember, if you fail tracking (like obedience and protection), you fail the trial.