Generating Random Number Within Specified Range

I'm using VB.NET 2008 Express Edition and I'm trying to create a simple program that will roll a number of dice I choose. It does this by generating a random number within a specified range (I'm rolling 3-sided dice in this case so I'm generating numbers between 1 and 3) and adding each number to a textbox to create a total of all the dice rolled so far.

This is my
Private Sub butRoll_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles butRoll.Click
Dim RandNum, i As Integer
Dim RandomClass As New Random()
'if at least one dice is rolled
If txtD3.Text > 0 Then
[Code] ......

Now the problem I am having is that although my random number generator is generating the right numbers (confirmed by checking the txtLastRoll textbox), when I add it to txtTotal, it seems to be getting another number from somewhere and adding that to my random number then adding it to the total and I have no idea how this is possible! txtTotal always starts as 0 but txt1 is not showing that. Normally I would just set txtTotal to 0 there but if I do that, I won't be able to add the numbers together. I've tried finding a pattern in the mystery numbers appearing in txtTotal but they just seem to be random.