Can't Play Slap-Bass Comfortable?

Ok, so i really need help on this one. Every time i go to play some red hot chili peppers or some funk bands song i always feel a bit uncomfortable when i start playing the 'slap'. Right now, the only bass i have right now is a shitty Richwood bass, It is good for the price but it is still kind of ****. I am not showing off or boasting in anyway or form but i would class myself as a lot better than most slap bassists around my age. It there anyway to stop this? Could this be my bass? I don't have much of a problem when i am really in the mood to play Slap-bass but hey, i am sure nearly everyone is better playing an instrument when there in the mood. Can anyone give me some advice on how to stop this? Thanks to anyone who answers.