Collision Issue Pinball VB.net 2015 - vb.net

Question

So I am making a basic pinball game using vb.net and am having an issue with the collisions that once the ball slows down a certain amount it glitches inside and then through the walls.
I am using a picturebox for the walls and the ball and am using the intersectwith(picturebox command to detect collision.
any help on how to fix this would be appreciated. Thanks
Bellow is most of the code: (pctball is the ball)
Private Sub Screen_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
DoubleBuffered = True
dX = 6 ' Pixels per timer tick
dY = 6
Timer1.Enabled = True
'array for colliding scores
For Each obj In Me.Controls
If TypeOf obj Is PictureBox AndAlso obj.tag = "Disc" Then
DiscArray(i) = obj
i += 1
End If
Next
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
If GameActive = True Then
Labelx.Text = PctBall.Left
Labely.Text = PctBall.Top
PctBall.Left = PctBall.Left + dX
PctBall.Top = PctBall.Top + dY
' check for ball hitting edges, reverse direction if so
If PctBall.Left < 10 Or PctBall.Left > MyBase.Width - PctBall.Width Then
dX = -dX
End If
If PctBall.Top < 10 Then
dY = -dY
End If
If LeftFlipper = True Then
FlipperDefaultL.Visible = False
FlipperUpL.Visible = True
Else
FlipperDefaultL.Visible = True
FlipperUpL.Visible = False
End If
If RightFlipper = True Then
FlipperDefaultR.Visible = False
FlipperUpR.Visible = True
Else
FlipperDefaultR.Visible = True
FlipperUpR.Visible = False
End If
GravityFunction()
ReboundAngle()
' If ball goes outside bottom
If PctBall.Bottom > MyBase.Height Then
GameActive = False
Game_Over()
End If
End If
End Sub
Private Sub Keys_Down(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
Select Case e.KeyValue
Case Keys.Space
GameActive = True
Case Keys.D
LeftFlipper = True
Case Keys.K
RightFlipper = True
End Select
End Sub
Private Sub Keys_Up(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
Select Case e.KeyValue
'Case Keys.Space
' GameActive = False
Case Keys.D
LeftFlipper = False
Case Keys.K
RightFlipper = False
End Select
End Sub
Private Sub GravityFunction()
' gravity
gravity = CollisionCount
dY += gravity
PctBall.Top += dY
End Sub
Private Function CheckCollision()
For Each PictureBox In Me.Controls
If PictureBox IsNot PctBall AndAlso PictureBox.visible = True AndAlso PctBall.Bounds.IntersectsWith(PictureBox.Bounds) Then
collision = True
CollisionCount += 0.1
For discCount = 0 To DiscArray.Length - 1
If PictureBox IsNot PctBall AndAlso PctBall.Bounds.IntersectsWith(DiscArray(discCount).Bounds) Then
score = score + 1
ScoreBoard.scorelabel.Text = "Score: " & score
End If
Next
Exit For 'Exit when at least one collision found
Else : collision = False
End If
Next
If Collision = True Then
Coll.Text = "True"
Else
Coll.Text = "False"
End If
Return collision
End Function
Private Function ReboundAngle()
If CheckCollision() Then
dX = -dX
dY = -dY
End If
End Function