Celtic Solstice Mystery Quilt #5 - learning about sizes

When I pulled out the (few) blocks I made for this mystery quilt so far I noticed that the sizes of the blocks were not all the same.
Measuring in inches is new to me, as in the Netherlands we use the metric system (centimeters) - and I have only 1 (!!) very old ruler with an inches scale on the back side.

For the first block I used Bonnie's free templates, and that worked fine.
For the second block (chevron) I tried to follow Bonnie's clues but I must have done something wrong, as the chevrons are larger than the triangle blocs.

I decided to cut a template out of card board for a 3" block with the 1/4" seam visible.
Now it is very clear how far I'm off!!

I'm glad I made only a few blocks so I didn't waste too much fabric.

I don't have any quilting rulers and at this moment I don't know whether I should buy inches or centimeter rulers. As those rulers are expensive, for now I decided to sit down and design my own paper templates for this quilt before I continue sewing.