those mars may have been in the leather before you started.
you might have been able to get those marred spots blended in with a leather spoon before you dyed it.
now that you dyed it I don't think you can get rid of those mars.
it apears that the color is kinda thin on the backside of the holster main body but your skirt should cover that up.
your holster looks better than my first holster did.
My first holster didn't fit the handgun that i was making it for. i could do nothing to fix the holster.
big question now is will your handgun fit into the holster?

you can use small clamps to hold the holster together and slip the handgun in to see if it will fit.
you may want to do this before you sew because you may need to add a spacer up at the trigger gaurd area of the holster.
the space will go between both sides of the leather opening the holster up for the trigger gaurd to slip in easier.
did you put sealer on it yet?
i found out the hard way, not to put sealer on the holster till its formed to the handgun.
i dunk my holsters into water then stuff handgun into holster and form it with hands till its the way i want it. let it dry for 1 hour then take handgun out and let dry overnight. then double check fit of holster to handgun. now seal with your sealer.
i put sealer on holster one time before i formed it. the sealer prevented the leather from drying uniformly. i got light and dark spots all over the holster from water not drying out evenly.
you did great for your first holster.