This may or may not help, but in regards to the recording aspect you could try punch in recording. Record a little section of the rap and if you hit a block just stop the recording right there then cut out the part where you hit the block but leave everything before it. Then you can continue on from where you left off before you encountered the block. It may take a little to get used to but if you do it enough you'll get adjusted to recording like that. Also, don't worry about the number of takes you need to get something that you think sounds good. The listener is only going to hear what makes it in so those takes that didn't make it into your song don't matter. Relax and record as many takes as you need to. Don't give up. If you feel like you just can't get it down or it's stressing you out just take a break for a little and try again later or the next day. You got this!!