The blueberries should work well enough, methinks.
Taste as it goes, and decide when to start drinking it yourself--a thief is highly recommended. Just, whatever you do, secret a bottle away for awhile and try it months after your stock is gone--you'll be amazed how much it's improved.
Using sugar (especially such a high %) is likely to have thinned the body and added a raisiny character. But since the recipe originally called for raisins, maybe that wont be too bad
. If it's rough the first time you taste it, tuck it back in the corner and give it another month or two. Age cure all ales (and meads, too!).