Weird heightmap painting issues

hello there

Im trying to use the new terrain api, to make a run-time terrain editor

using this code:

 Material mat = TerrainPaintUtility.GetBuiltinPaintMaterial();
 
 
         
         BrushTransform brushXform = TerrainPaintUtility.CalculateBrushTransform(terrain, new Vector2(0.12f, 0.07f), 150, 0);
         PaintContext paintContext = TerrainPaintUtility.BeginPaintHeightmap(terrain, brushXform.GetBrushXYBounds());
 
         
         // apply brush
         Vector4 brushParams = new Vector4(0.004f * Time.deltaTime * BrushStrength, 0.0f, 0.0f, 0.0f);
         mat.SetTexture("_BrushTex", texture);
         mat.SetVector("_BrushParams", brushParams);
         TerrainPaintUtility.SetupTerrainToolMaterialProperties(paintContext, brushXform, mat);
 
         Graphics.Blit(paintContext.sourceRenderTexture, paintContext.destinationRenderTexture, mat, (int)TerrainPaintUtility.BuiltinPaintMaterialPasses.RaiseLowerHeight);
 
         TerrainPaintUtility.EndPaintHeightmap(paintContext, "Terrain Paint");
         TerrainPaintUtility.ReleaseContextResources(paintContext);

for some reason when i try to paint height it gives this weird shape

even though i used this brush texture:

even weirder is that the pattern (the heights of steps) seems to be random

the brush texture is imported as R 16 bit

does anyone have any idea what could be causing this?