Hmmm I'll have to break the bad news to you :< But unless some miracle happens the HC will not carpet... in fact it may struggle to stay alive. however the crypt will do well. if you really want to give HC a chance to grow out... you will have to drain most of the water and bring the light closer to the substrate. a better ( and more expensive ) carpet for a low light tank would probably be flattened marimo moss balls...HM (not giant baby tears) will also make a good carpet under highlight without CO2, but you will also risk an algae take over :O.
likewise dwarf hair grass "belem" is also a good candidate. it is spreading over my 2.5 nicely.
mind you I have about 30ws of cfl lighting over a half filled 2.5 gallon tank which leads to better light penetration and access to atmospheric CO2.
HM (left) E. belem(right)
edit: sorry more plants come to mind...
you can also try Hydrocotly Sp. Japan, however you will have to do a dry start to have it carpet faster..otherwise you may end up having to manually shove the plant back down into the substrate. but that one is a nice easy plant that is low light tolerant