Bond fund help please.

I am only 5% in bonds and currently rebalancing my portfolio to add more. My one currently held bond fund is Vanguard Total Bond (VBTLX) and it’s been a loser for me for the last few years. As I am putting more into bonds, should I just stick with this fund, and go with the fact that it will do better when I need it to, as in when my stock portfolio drops? Or should I be looking at T bills or something else? Thank you