First one sounds like 'pelo' (hair), second one like 'pero' (but), and last two like 'Pedro' (Peter). An I'm sure you know, this is a challenging sound for Chinese native-speakers. So be patient, continue practicing, and don't get too obsessed about it, just try to communicate and speak the language. Also, always practice the sound in context with all the vowels: Ar + e, i, o, u; Er + a,i,o,u; Ir + a,e,o,u; etc ...