How do you say "I'll be a little late"?
There are many ways you can say this. Some examples:


我会迟到一点
我要来得晚些
我会晚来一会儿
我会晚一点到达


You can also say it your way. It is not really necessarily, but I would add 要 or 会. I also wouldn't use the 吧 in this sentence. So something like


我要晚一点到
我会晚一点到