Sounds like the blue gauge is the right one if it is marked -4. The color is immaterial--mine is copper to match the 1/8" cleco. To use it place the hole over the shop head. This checks the diameter--the head should barely fit in the hole to not fitting at all (depends on the brand). Regardless, if there's any play then the diameter is too small. Before doing anything, use the notch to check the height. With the gauge perpendicular to the shop head try and slide the gauge over the rivet and through the notch. If it goes through, you over shot the rivet.
If the rivet diameter is too small, but the height is fine, just hit the rivet again. If the diameter is too small and the height is already too low, then you probably need to move to the next size rivet (length). You will run into this. Even though you use the rivet called out in the plans, sometimes it's just too short to properly form an adequate shop head.
Looking at your photos, my only concerns are the rivets on the hinges. Hard to tell from the photo, but they look way overshot.