Should I be worried about this gap in electrical conduit?
I see 3 problems:


The gap, as you noticed.
One of the conductors' insulation is damaged (I think - it's not obvious from the picture)
That's EMT, which is not a good choice for burial. The couplings are not strong enough (as you can see) and they're not waterproof. The tubing can rust away below ground. It is technically allowed, though, per NEC 358.10.


I'd recommend replacing it with PVC, which is very durable and easy to work with. If you do this, I suggest oversizing the conduit a couple sizes, to make pulling the wires easier and to leave room for future upgrades. And while you're at it, put a subpanel in the garage.