You maybe have a shitty bidet, or its settings need to be adjusted .
Also there's a bit of technique - you gotta move around a bit; work the spray around to get everything.

Use your hands and wash with soap. Then use toilet paper to pat dry afterwards. That’s what I do and you can’t get any cleaner than that.

Try Adding a light abrasive to the Water. You can find bulk sillica at your local bodyshop.

Maybe you have low water pressure? It should feel like a tiny hose.