Build system can't find correct python even with help

I'm trying to build Boost 1.74.0 on Amazon Linux 2. AL2 defaults to including python 2.7, but I've installed Python 3.7, and informed Boost's bootstrap program about this preferred Python. But it's failing because it's still attempting to build libraries for Python2.7, and I don't even have the development files installed for that. So, as above, it can't find pyconfig.h. But I told it to use 3.7, and gave it the include and lib paths to boot.

The way Python is installed on this is that /usr/bin/python is 2.7, and /usr/bin/python3 is 3.7. Somewhere I haven't found, it's just using the "python" default and not using the "using" declarations I gave it. HELP!