Will this hurt my dog?!?

Ok, so, I made a roast beef sandwich with cheese and mustard.... and obviously bread haha. But yea my mom called me outside for a couple minutes because she needed something from inside so I got it and then I had to help her for like 4 or 5 minutes, so when I came back my roast beef sandwich was gone.... Obviously my dog ate it because he would do that it's happened with minor things. I haven't told my parents yet, because they're just gonna yell at him and if it's not gonna hurt him or do anything bad to him I'll just save him the senseless yelling.... although he does in a way deserve it. But will it do anything?!?