If you are not retiring for 20-30 years, there's not much risk.
If you mean you are retiring sooner and the 401a will not be withdrawn from for another 20-30 years, then this $23.5k account is a small portion of your overall stash, and it's your overall AA that matters.
Beware. Nobody seems to care about diversification until an entire sector gets wiped out, like tech in 2000, finance in 2008, and energy in 2015-16. Contrarians outlive trend chasers.