suggestions
Here ae a couple of considerations: (1) Chainsaw chain stretches, especially with first use, and may require several adjustments before it stays put.
(2) Are you able to LOOSEN the adjusting tab? If the tab loosens but does not tension adequately, you may have a chain that is too long for the bar. (3) take the saw to a saw shop and ask for their help...be prepared to be a little embarrassed, as it is not likely the saw's fault ( I did the same thing with my new Stihl!)