Nightowl
As you progress you will find that some pieces will be a bit more difficult. These will be the ones which teach harder concepts. The ones which repeat those concepts so they become ingrained will be easier.
Not to start another round of "speed kills...," but if you want to get faster you must practice for speed and not accuracy. No auctioneer was born babbling their sales nonsense, they all needed to learn how and what to say and then say it faster. And, while not everyone can sling the lingo like an auctioneer can, that doesn't mean you have to live life in the slow lane chanting at a walking cadence either.
Practice triplets. Practice full measures of 8ths and 16ths. Practice your scale and arpeggio runs. Push for speed, your fingers will fumble at first, but you will get faster. Then pull back from full throttle and concentrate on not hitting wrong keys or being out of sequence. You will be faster. Then push for more speed again and repeat the cycle.
Now play something you know and which is extremely easy. Play it as fast as you can. Again. Again. Again!
Now play it at tempo. And be amazed at how difficult it will be to slow down.
