What do these red crosses mean
They indicate a "violation" of some kind.

I don't know Circuitmaker, but in Altium, you can right-click on the object and one of the options in the pop-up menu will be "Violations..." which will tell you why there is a violation.

In this case, it's possible you didn't assign the tracks to the GND net, so you have copper assigned to the GND net (the 3 pads) touching copper assigned to "No Net", which is treated as an undesired short circuit. This could happen if you used "Place Line" instead of "Place Track" or "Interactive routing" to add the tracks.