There are a few different ways to manage a microstrip line that is larger than the pads.
It’s not uncommon for microstrip transmissions lines to be thicker than the connection points. In this case, the trace can be tapered at the module / connector pin. It should not have a large impact on impedance to have the trace tapered ~2mm at the connection points. Especially at the lower frequencies, in the 400MHz band.
The microstrip width can also be narrowed by putting the ground plane on an internal layer, reducing the height to the microstrip, resulting in a smaller trace width.
Another option is a Co-Planar Waveguide (CPWG), which allows for more precise control over impedance and smaller trace width. This adds a ground plane on the top layer, on either side of the antenna trace. The gap between the plane and trace can be varied to make the trace width smaller.
AppCAD is a free program that is useful to help with transmission line calculations.