At 50 MHz the free-space wavelength λ is:

Your 82 mm trace is therefore:

Rule-of-thumb: if a trace is longer than ≈10 % of λ it behaves as a transmission line and benefits from controlled impedance. At only 1.4 % of λ, this run is electrically “short” at 50 MHz, so you do not strictly need to impedance-match it.

If you’re worried about very fast edges (digital rise/fall times), use the rise-time rule instead (e.g. trace length > tr/10). Otherwise, you can leave this trace at your standard width.

Here’s what the Flux documentation says about setting up controlled-impedance traces:

“## Configuring Impedance Control

There are two ways of configuring impedance control for a part: