Mistakes are going to happen behind you. The younger you are, the more it will happen. You can’t let it get to you mentally. Errors increase pitch count, pitches per inning, fatigue and stress. Believe me, the guys don’t want to make mistakes any more than you want to miss your spot with each pitch. As long as your defense is focused and prepared, mistakes will be minimized. Most errors are caused by lack of focus and those are inexcusable and I would agree with @Zita_Carno about extra fielding practice.
I have two pickle buckets filled with 65-70 balls each. Each infielder gets two of these per practice. Attack the ball, gather the ball and yourself, get momentum toward the target, and get into throwing position or feeding position, then toss the ball into a pile just into the outfield grass. That usually keeps the error count down for my kids.
If your coach isn’t giving each infielder at least 100 ground balls per practice, he’s not helping his pitching staff. It only takes 8-10 minutes per bucket, so in about 15 minutes per player you can easily get in a ton of grounders. In 45 minutes, using both fungo circles, you can get through all 4 infielders and two reserves. This can easily be done during batting practice if you have a couple of screens.