Am I wrong?

Samantha
Okay so I am a stepmother to my husband's basically 7 year old son (he turns 7 in this upcoming July) . His mother is in and out of his life when she wants to but I have raised him since he was 3. I am currently 25 weeks and 3 days pregnant with my son's little sister and he is thrilled to be a big brother. So as of late my MIL thinks I am too strict on him and I don't think I am because I let his do a lot of what he wants and if I say no I am the bad guy. For instance my son wanted Ice Cream at 8 at night and my personal opinion is that it's too late so I told him he could have some fruit instead. So my mother in law thinks that I am too harsh on him and that aims don't let him be a child and I do. I give him a lot of freedom but if he is disrespectful his freedom is a little limited as punishment. Disrespectful being that if he doesn't get what he wants he throws huge tantrum gets aggressive and screams and cries and doest listen to anybody what so ever (I send him to his room to calm down and get himself together) am I wrong for doing these things?