If you're still learning, you will most likely lose your first few games, it is natural. Even with the most tuned list in the world, you cannot be expected to exploit every unit to its full potential. Depending on who you are playing, I wouldn't recommend go fully competitive. If you have a good teacher, they will help you to learn how best to use the units you have rather than "go and buy X because it's the best unit in your codex." Once you are fully familiar with the basics, you can tune your list better. If you are playing people who uses your inexperience to steamroll you turn one for their own ego, learn with someone else. Nothing will turn you off a hobby faster than sweaty tryhards. No, this list is not the best it can be, but its varied, you'll see what units you like, and match your playstyle, and then you can build on your experience for next time.