To be honest, I think it's simply impossible to gain native level whatever you do in 8 month. Good expectation would be a brave beginner with manageable communication - for some that's admiring level, and for some others that's just stuttering bables. It just depends on you. If you manage to keep conversing only in vietnamese without resorting to english, after 8 months, I would admire you and would take you as my role model, even though your vietnamese is wierd or awkard or anything like babbling stutter, if you just keep pleasant conversation.
Fluency isn't about perfect vietnamese, but your ability to communicate anyway.
I also had some unreasonable goal thee years ago, but after every effort I'v made, I'm still terrible beginner ... just cannot continue two questions away, sigh. Am I a terrible learner?
Believe me, I'm a language holic with 6 languages. I'm constantly trying to get better way of learning. I had tried almost every thing I can do .. well, I'm quite busy korean, and I don't have much time, but I'm very aware of how much minutes I spend each time, so I can very clearly say how long I've spent in total. If you pay every minutes during the whole months... you may get high enough level, but vietnamese may clearly tell you are a foreigher. Without some kind of musical sensitivity talent, you'll never achieve that level.
But please you just try, I know that you aren't talking about pertectionism. Perhaps eye popping, courageous, mond boggling success stories are abundant. Just try.