Diana N Tech barrel issue

G,Day from sunny Australia. Ive got an issus of sorts with my new ntech 340 in 177.I recently installed a diana ZR recoiling scope mount with a niko 3 to 9 power scope..

The only way to zero in the scope has been to install 3 x aluminum shims from a drink can onto the front scope mount. Thjs obviously raises the front of the scope and then to adjust it the rest of thr way the elevation turret is turned all the way in..

If i sight along the rifle it appears that the barrel is angled up . The gun still shoots great with good power .When i first put the scope on it was new out of the box with elevation adjusted to the centre my point of impact was about 18 inches above my point of aim at about 25 metres. . Should there be a need to add shims as both the gun and scope mount are new Diana products. . The gun has never been dropped or damaged in any way. HAS ANYONE GOT THOUGHTS ON THIS.
 
If the gun groups well with good power then I would simply bend the barrel down to get it close to POI on a centered scope. The barrel is very easy to bend. Just go slow because a little goes a long way. Have had to do this with a few of my Dianas and accuracy have stayed the same. As said above you are using a droop compensating mount but you also said it shoots high with open sights. Either send the gun back, get adjustable rings or bend the barrel.