There's nothing to worry about unless you hear detonation (knocking or pinging sounds that you haven't heard before), especially when accelerating or climbing hills.

Modern cars have sensors that retard timing if the engine knocks, and most modern "premium fuel" cars can be operated without problem on lower octane fuels. They just might not feel as peppy because of the retarded timing.

Several of my friends switched their "premium fuel" engines to unleaded regular at my suggestion (I got tired of hearing them whine about the extra cost of premium fuel.), and they have not experienced any knock and can't tell any difference in performance or fuel economy. A boosted engine might have a more noticeable loss of pep than a naturally aspirated engine.

If you don't notice knock or any loss of performance, keep using midgrade or even try regular and see how that works.

Duke