Help placing light object on dark background without background affecting the light colours?

Photoshop CC 2018

Windows 19

Hi All.

First time posting here so be kind.

I have been wrestling with this issue for a few days and web searches have been unable to offer a solution so I wondered if a kind soul here may be able to put me on the corrct path (pun intended).

I have Logo that I have designed using pastel colours that I wish to place over a darker single colour background but when I place the background it shows through the logo affecting the colours. The effect is as if I have turned the opacity of the logo layer down to say 50%. ( I have checked at its set at 100%).

This is the process I have tried:

To create the logo I used various different layers which were all merged down to a single layer when I was happy with the logo and its set to Normal.

I then used the Magic Wand Tool to remove the background space around the logo (select > delete).

I then added a new layer and using the Paint Bucket tool filled it with my choice of background colour. 

In the layers tab the logo is the top of the list with the background below it.

When I make the background layer visable it shows through the logo instead of being blocked out.

I tried changing the Logo from Multiply to Normal and this does stop the background showing through but it leaves a 3 or 4 pixel thick white outline around the logo which is quite noticable.

The reason for this my be due to the fact that the outside edges of the logo are not hard edges, they are graduated so the the edge fades from colour to transparant and I believe that when I use the Magic Selection Tool Photoshop is placing the "marching ants" at the very edge of the graduation.

What I am trying to achieve is that Photoshop allows the background to show through the graduation but only upto where the logo colours become solid.

I hope this makes sense and any help would be very gratefully received.

Thanks.