If you're not done with the cycle, then specific gravity isn't too big of a concern. But if you want to stabalize it w/o a water change, toss in couple table spoons of instant ocean or other salt mix into your topoff water. Add this until SG comes up to where you want it. BUT, before you do that make sure your temp is consistent from one reading to the next. SG is effected by temp.
I have a 5.5 AGA invert tank and never really expect to have the same levels from one week to the next. Avg daily evaporation swings my SG + .02 . It's a great "Vacation Home" for my snails and shrimp from my main tanks.