Google Maps, or any other mapping app intended for auto or bicycling use, will only route you on known roads, not a Camino path, per se. Only where the Camino has you walking on the verge / shoulder of a road, will it be accurate.
If you must have this sort of detailed tracking capability, I recommend the very inexpensive but very comprehensive
Wise Pilgrim Guides series of apps and hard copy guide books. The apps have an offline mapping capability that uses the smartphone 'pinging' to cell towers to establish your path and routing along a downloaded topographical map.
This nearly as good as a specific GPS only app, like
Maps.me, but contains so much more useful information. Check it out at
www.wisepilgrim.com to verify exactly which app you need, then go to the Android or Apple app store as appropriate to download the app.
Also, you can buy the hard copy guidebook here in the forum, at the Camino Forum Store / Casa Ivar. See the blue rectangular button to the right of this page...
Hope this helps.