Create points along line and apply a 90° offset to them - pyqgis

Question

I want to create points along a line (works!) and then additionally move the points by a certain offset (perpendicular to the line) with pyqgis 3. See this sketch for further illustration:

My current python script does following: It basically interpolates the position at the certain length of the line and then it constructs the position of the offset point by triangulation. The script works so far, but the drawn point has a slight deviation in it's x coordinate (see figure 2).

My code so far:

def createPointsAtOffset(distance, offset, geom):
length = geom.length()
currentdistance = distance
feats = []

point = geom.interpolate(currentdistance)
fet = QgsFeature()
fet.setAttributes([currentdistance, offset])

if offset is not 0:
    xy = point.asPoint()
    alpha = (math.degrees(geom.interpolateAngle(currentdistance)) - 90) # return in degree
    # create delta x and y via triangulating
    delY = math.cos(math.radians(alpha)) * offset
    delX = math.sin(math.radians(alpha))* offset #12
    delT = math.sqrt(offset*offset - delY*delY)

    pointX = xy[0] + delX
    pointY = xy[1] + delY
    fet.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(pointX,pointY)))

else:
    fet.setGeometry(point)

feats.append(fet)

return feats

def pointsAlongLineOffset(distance, offset):
# Create a new memory layer and add a distance attribute
vl = QgsVectorLayer("Point", "distance offset nodes", "memory")
pr = vl.dataProvider()
pr.addAttributes( [ QgsField("distance", QVariant.Double), QgsField("offset", QVariant.Double) ] )
layer = iface.mapCanvas().currentLayer()
# Loop though all the features
for feature in layer.getFeatures():
    geom = feature.geometry()
    # hier muss dann eine schleife durch alles distance offset paare durchgehen
    #features = createPointsAt(distance, geom)
    features = createPointsAtOffset(distance, offset, geom)
    pr.addFeatures(features)
    vl.updateExtents()

QgsProject.instance().addMapLayer(vl)

# example for the image above:
pointsAlongLineOffset(1.2,2.5)

I think my error is that I use a wrong angle in the triangulation part. In the example the line is tilted about 6° from east but when I insert about 12° into the calculation of delX it works? Am I missing some kind of deviation from north or is my approach completely wrong?