The human brain is pre-programmed to learn language. Your accent (and vocabulary and grammar in general) will improve with time and exposure to English as you live in this environment because your brain, all on its own, will do its best to "tune in" your English to more closely resemble the English spoken around you. Be aware that this acquisition of language skills is something over which you have limited conscious control. You need to provide yourself with opportunities to receive a lot of language input, you have to do your best to use the language (what is called language "output"), and then you have to let the unconscious grammar-construction apparatus of your brain do the work.
There do appear to be some limits on how closely L2 pronunciation can approach that of an L1 speaker without specific accent training. And these limits depend on multiple factors: the two (or more) languages involved; the learner's age; the learner's personality; etc. If you really want to work on your accent, you can find an accent reduction class or tutor in the US or in your home country. The work will not be easy, or quick, but it can be done. Think of all the now-famous Hollywood actors who can talk like us gringos, but who sure weren't born here!
For more fun reading on language learning and language acquisition, visit the website of Steven Krashen at:
Books and Articles by Stephen D Krashen
For some fun reading on why we all struggle with perfecting our accents in that second (or third or whatever higher number) language, read just about anything by Patricia Kuhl who is on the faculty at the University of Washington. I'd suggest starting with "A perceptual interference account of acquisition difficulties for non-native phonemes." published in the journal Cognition, vol. 87 in 2003.
Wishing all of you all the best as you confront the peculiarities of American English!