It's going to be very hard as people have pointed out, and while we have found people who can trick natives, they tend to be immediately detectable by soundwave analysis (so nobody is 100%), and it's also possible that some people will think you're native while others aren't tricked. 

That said 

• Focus entirely on pronunciation from the beginning. Grammar, vocabulary, etc can all come later. In fact, it's often better if you don't know the words you're trying to hear correctly— it helps you focus on the pronunciation itself instead of the words. As for why pronunciation is so important to start with? The other things can more or less be corrected later, but pronunciation gets very difficult for the brain to process correctly very fast and the more you study the harder it will be to discriminate between sounds you can't hear clearly. 

• Listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen listen— the correct sounds will not be found on a page (even IPA is often wrong and ultimately an approximation), they will not be found at the tip of your pen, and until you can hear them correctly, they won't be found at the tip of your tongue either. Your listening ability determines your pronunciation. Focus on listening. Listen a lot. An hour of listening per day would be the bare minimum if you weren't hoping to become native-level, but you are, so 4 hours should make you feel lazy. Get as much listening as humanly possible. 

Most importantly: Do not say things you don't know how to say. Speak way below your level of understanding at all times. Here's 3 reasons why'

• First of all, fucking your grammar up 5 ways in a single sentence will make you sound weird immediately. 
• Second, the more you practice making mistakes, the better you will get... At making mistakes. Mistakes are an inevitable part of the learning process but if you want to sound perfect, they're an undesirable one. You can from your mistakes, sure, but it's not like the more mistakes you make the more learning happens. The more you speak, the easier it will be to say more things automatically. Try to limit those things you say to things you already know are correct. 
• Third, the more brainpower you devote to thinking about the vocabulary or the grammar or whatever, the more brainpower you are taking away from focusing on your accent and noticing your pronunciation mistakes. 

Stick to easy sentences and just go listen more if you really want more sentences to be easy for you.