The previous replies are all solid advice and explanation.
I can add to some of it a bit. I will assume you're learning it from "Mechanic". DMs bottom deal is IMO brilliant technique and I have heavily adapted his technique and advice to my own.
First, don't get discouraged. I don't know how long you've been working on your BD, but it does take a LOT of time and practice to put it all together, so be patient and now that you know the technique, continue to work these trouble spots, you will overcome.
Second, take a moment, go back and watch the entire section on fair dealing on through the bottom deal. Just listen and watch, no deck, no interruptions. There is a great deal of tidbit info on the hows and whys regarding the subtleties that can be overlooked the first few times through. Most importantly, Daniel speaks about adjusting your grip to fit your hand and making it your own. SO IMPORTANT! Use his techniques, but the grip is not set in stone and you, like me, will find that you may need to adjust a bit to make it all work correctly, never forgetting the techniques as he teaches them. Essentially keeping your middle finger on/at that corner of the deck is crucial. It, along with your index finger provide the shade for your ring finger to do the slide with no flash. Concentrate on keeping your deck hand index and mid finger immobile while moving your ring finger like Daniel shows, almost like the "Spock" hand from the old Star Trek TV show. That's not the exact motion, but it's close.
Specifically on your questions, I have a feeling your top card issue may, as another suggested, be related to the pressure you're using (too much?). It also may be where you are placing the thumb on the top card itself to push it off. Again, review where DM places his thumb for the push off and keep working at it.
An often overlooked issue: Try using a different deck, or a broken in deck, or a new deck, or just a different brand. Sometimes that can assist with learning the fine points. On that point, as you learn and practice, I STRONGLY recommend you do exactly that, use various decks in various degrees of usage. It not only helps you to learn, but gets you ready to be able to pick up any deck and perform undetected in any game.
Lastly, you are correct, these are all issues to be expected when learning a bottom deal so don't get frustrated and don't give up or look elsewhere. It sounds like you have put some time in and are on your way. Don't give up, keep at it, and feel free to adjust the grip to fit your hand within reason.
Whatever grip you settle on, as DM says, make sure your fair deal grip matches all your false deal grips.
DM has a brilliant approach to deck mechanics and there aren't many, if any, wasted words in his dealing instructions particularly. Everything he says is important and useful. People have preferences and again as another indicated, it's all about what's best for you.
That said, anything worth learning is worth putting in as much time and effort as you can throw at it. I assure you that if you keep at it, you will get it, and you will look back and remember the days you struggled with a proud grin on your face as you deal undetected bottoms, seconds, and even Greeks.
Good luck to you and keep up the work. It's worth it and DM has both the techniques and philosophy that bring home the money.
