Choose a suitable board stack-up that supports 75-Ω single-ended trace and 100-Ω differential trace routing on the top layer of the board. This is typically done with a Layer-2 ground plane reference for the 100-Ω differential traces and a Layer-3 ground plane reference for the 75-Ω single-end traces.
Maintain a distance of at least 5 times the trace width between signal trace and ground reference if they are on the same layer. This prevents unwanted changes in the characteristic impedance.
Maintain a consistent ground plane reference for each high-speed trace from source to end-point. Ground reference discontinuities lead to characteristic impedance mismatch.