It's likely that you'll mess up the execution MANY times at first, and your success rate only improves as you grind solves. My first 100 solves probably had 10-20 successes MAXIMUM. It can definitely be frustrating as you first get used to this method, but you'll get it with practice!
If there is a consistent issue when executing solutions, it may be a good idea to double check your memorization. There's a 7-Simul memo trainer you can use to ensure you're correctly performing calculations (link below).