Uh.....No. A standard 55 gallon is 48" long, 12" wide, and 18" deep. If you have anything other than that, it's either not a 55, or it's not a standard 55.
the brace should be easy to glue or use jbweld to fix, it's not structurally comprimised based on the photo. Also most 55g are tempered so little bowing will happen even on a completely broken brace. In fact most plastic braces provide little support at best. Glass or metal braces work best.