Go over your work.
DO NOT use stop leak
If you used aftermarket heater pipes, they can be tricky to install without leaks. I try to use OEM pipes, but will use aftermarket pipes with OEM o-rings, which seems to work out. I also test them after install before putting intake manifold on, by hooking up all coolant pipes and hoses, install a special gutted thermostat housing I have, fill with distilled water and pressurize with <20 psi
In your case I would pressurize the cooling system - I use a compressor, but you can use a coolant pressure tester from harbor freight- and shine a light through the intake near were heater pipes enter block. check for leaks. If they are dry check the rest of your work.