Welcome to the forum, miguel30mini. Are you talking about the gap between the end of the stock and the gas block ? One of my Mini-30's has a gap like that, it's no big deal. Only other thing I see in that pic is the gas block is scratched up where the swivel goes.
Make sure the gas block screws are torqued down in a criss cross, alternating pattern, and that when you are done, the gap on either side looks the same.
Proper torque is 25-30 inch pounds ( not foot pounds). Lacking a torque wrench, just tighten them hand tight, then another 1/4 turn with an Allen wrench.
I handload, so I can adjust my loads to the individual gun to find the most accurate load. One of the members over on perfectunions Mini forum reloads, but doesn't load for the 7.62x39. He has a big stash of Silver bear ammo that he likes, and found he can tweak the gas block screws a bit at a time, and tune the gun to the ammo. Kind of the opposite of what I do. which is tune the ammo to the gun.
You can see a bit of gap between the stock and gas block on my stainless Mini-30 in this pic.