It's not really your fault. Vietnamese P, T, K/C/Q are unaspirated, which means that there is no puff of air coming out after them. If you pronounce the English word "pin", you could blow out a candle in front of your face, right. If you put your hand there, you will notice. Now say "spin" — you notice, (almost) no air coming out. That is the right sound. And if you pronounce this sound without the s- in front of it, it does sound a bit like "bin" (or "bean" maybe), because English doesn't have these unaspirated stops at the beginning of words.