1. This is normal! Accuracy will come with time and practice, and even then it will falter intermittently - the most important thing you can focus on at this stage is drawing confidently with your whole arm. It sounds like you're taking enough time to plan out your lines, so just keep doing that. If you miss, don't worry, you have plenty of practice in your future!

2. It can be quite tempting to compare your work to that of others, but this is a false benchmark of your progress. The only true measure of your progress comes from comparing your work to your previous work - a week ago, a month ago, a year ago. Here you can see meaningful, measurable, specific improvement which you can point to. Not only does this help you understand what you've improved on mechanically, it also helps to highlight changes in your ability to evaluate art, which itself is a separate skill. Your best drawing that you were super proud of a year ago might look much worse after you've learned more about perspective, lighting, color theory, etc. That doesn't mean it was a bad drawing, it means you've gotten better at perceiving and evaluating your own work, which is something to be celebrated.

Keep up the good work and don't let mechanical errors stand in your way! Take your time, draw them boxes, and be proud of what you've accomplished! I think you'll find that your first 5 boxes will look quite different from your last 5. Good luck!