I nominated a wayspot and it was accepeted. But now the place I nominated appears as a powerspot rather than a pokestop.
Welcome to the forum!
If it became a Power Spot, then it was not eligible to be a Pokestop.
I know the prompt tells you that you are submitting a “Pokestop” but you are actually submitting a Wayspot to the database. The Wayspot can only become a Pokestop or gym if it is alone in a level 17 S2 cell. This is a good article about S2 cells and PoGo: https://pokemongohub.net/post/article/comprehensive-guide-s2-cells-pokemon-go/
If you would like to leave the title and location, someone here can check if this is the issue. But do be aware this is a public forum if you would rather not reveal your location.
If it turn into powerspot, probably another wayspot already exist within same cell. Read above for s2 cell rule. Each cell can only host one pokestop/gym. Any other unused wayspot will probably become power spot. Thats normal