Other mistake: At the end, when Bill and Ted reunite with their wives, one of them mentioned hearing Ted say something about distributing instruments to everyone throughout all time. However, Ted said this a minute or 2 before they arrived. We even see the phonebooth they are in land after the statement was made. Therefore, there was no way for his wife to hear him say that.
Other mistake: On 22's name-tag wall some of the names repeat themselves. Yossi Mizrahi and Itay Cochabi can be spotted twice, once towards the center and once towards the right side of the screen. There might be more.