It would be strange if it only happened to you. But this happens with EVERYONE. Very few of us can master a native's way of speaking a language. The best way for you is to listen to english so much that your brain is attuned to speaking and pronouncing it that way :
1. IMMERSE yourself in English. Try to think English whenever and wherever. In your mind, try to say expressions that you use everyday in English.
2. TALK to people who know English. Italki is a good website for the same. Just add language buddies here. Teach them Indonesian and learn English from them. Add them on Skype and try to have a conversation. Everyday you will improve.
3. LISTEN, to songs, videos, shows and anything that make your ears attuned to catching English words. The toughest part of a language is to understand what the native speakers speak. Sine the words flow at an amazing pace, it is difficult to distinguish between words. But slowly, it will become a habit.
Also when you keep listening to people, your English will automatically begin to improve its way of speech.