Never give up dude! If rap is what you seriously want to do then you need to keep at it:
"Nothing comes easy it takes much practise".
When I listen back to the tapes I had when I first started out they were absolutely terrible! It really makes me cringe to think I was showing people them back in the day.
But the more you keep practising and the more you keep rhyming the better you'll get. Its simple logic, the more you do something the better you'll get at it. If I compare what I'm doing now to what I was doing when I started out, I like to think that there is a huge difference!