Travel Days

with the 7d in 1M pass you can travel under use of the pass on 7 days to choose by you. for the 8th day check out which leg is the cheapest by normal ticket and buy that instead of using a travel day there.

So am I correct in thinking I have purchased Reservations for 8 days on  my trip but before travel I have to asign 7 of these days to the pass and then just purchase a ticket to match the 8th reservation

When you travel in Switzerland you don't need any reservations, reservations in Switzerland are a waste of money. Just enter the train as a journey in the Railplanner and activate it just before boarding the train. 

​@Pdaddy 

If you have mandatory reservations for long distance trains (e.g.TGV in France, Frecciarossa in Italy or Eurocity between Switzerland and Italy), you must use a travel day of your pass. It is not possible to buy only a ticket for these reservations.

You can add as many days to your trip as you like, but you can only activate 7 travel days. You can't activate an 8th day. You'll have to decide yourself on which day you buy a regular ticket (usually on the cheapest day).