I learned a lot from this game's instruction, Petit Professor, and from Miiverse, mostly from Oscar. xP
You don't really need all those prints. You can just overlap your text with just spaces, like so:
(? is another way to Print)
Locate 20,15 ?"Hello there!"
Wait 100
Locate 20,15 ?" "
0そうだね プレイ済み