Your mistakes are probably coming from a poor right hand technique. Here are some things you can do to work towards a better overall sound quality and versatility. ( and I think it looks cool too
1. Keep your thumb extended directly out(like an extension of your forearm)
2. Keep your middle and index fingers near the next two strings, ready to Pop them up when you need to.
3. Make sure that when slapping you are over the end of the fretboard, this will give you the deepest, growliest sound.
4. When slapping with your thumb, try to restrict your movement while still keeping your notes deliberate and clean. Most new players will tend to bounce their hand around all over the place.
5. Use a down and inward motion with your thumb, what I mean by this is that you shouldn't recoil clean away from the string. You want your thumb to push through your string and land for a split second on the fretboard. This will give you a bumpin' thump.
6. Stay loose and relaxed. You'll never develop what they call "pocket" if you stay tense and get yourself stuck.
7. Watch videos of the greats (mark king, les claypool, victor wooten, etc.) NOT FIELDY OR FLEA. Immitation is one of the biggest things I have found to help myself grow as a musician.
8. Most important of all is the most basic rule of anything you will EVER do. Practice makes perfect.