I rarely see an adult on a frame that is too big. Most adults are on frames that are too small, but some owners of "too small" bikes THINK their bike is "too big" because the bars are too low, making the cockpit too long, streching the rider out to an uncomfortable extent
If you can stand flat-footed over your bike without pain from the top tube pressing into your crotch, it is unlikely the frame is too big. Getting a good fit requires knowing your ideal saddle height, bar drop, and cockpit length. After you dial in a fit to within about 1/8th inch on those three dimensions, your bike will feel great while riding.
The road bikes that fit me best (at 5' 9" 3/4 inches tall) are in the size 58 to size 60 range). But, by dialing in saddle height, bar drop, and cockpit length, I can get an equally good fit on bikes in the size 55 to size 62 range. But, if a frame is waaay too small, getting a good fit requires an extremely tall stem, which can impact the handling of the bike.