Were my airplane's wheels under-inflated?
It's absolutely normal. Above is how the manufacturer even depicts the nose tire in the airport planning manual (.pdf, page 42).

The pressures are checked by line engineers typically before leaving the hub, as well as an inspection by a flight crew member before every flight.



While not available on the CRJ900, there are many jetliners that have tire pressure sensors. See:


Do airliners or business jets have brake temperature sensors? (image of such cockpit display)
How do tyre pressure sensors in aircraft work? (how they work)