What to cast with to fill 45mm over 3m2

[Andreas_kalmar]

Wrong ju should be a35mix

 

[olofh]

Wrong, it should be a35mix

A little expensive but thanks anyway

 

[Peter2400]

A little expensive but thanks anyway

Ten bags of floor compound and some primer will probably solve that cheaply and well.
Reinforcement I would probably skip.
https://www.byggmax.se/gjutning-och-husgrund/cement-och-bruk/golvbruk-25kg-p18262