Hi Casper, congratulations on finishing the assigments for lesson 4! For Arpeggi di Tre Note, you can slow down the whole piece, to make the 'easier' early parts the same speed as the 'harder' later parts. You can also just practice the harder parts first to make the chord changes smoother (it will still be tough because your fingers are relatively short for the guitar you're using. Don't worry it will get easier
Good job with the Valse and with memorizing it! Sorry can't comment on the E minor because I have not tried it.
The way you hold the guitar and lay the scores down in front of you remind me of myself when I started playing around your age. If possible, try to get a music stand so you don't have to crane your neck, and hold the guitar in the upright 45 degree position, it does make for easier playing.
Great job and am looking forward to more of your recordings. Have fun and keep playing!