I cut my hair short yesterday. It’s a big change, but I like it. I have nothing to do today, so I’m going to my grandparents’ house. We're going to have lunch together. "I cut my hair a lot" isn't necessarily wrong, but it sounds strange as "a lot" implies that you also did it frequently or over a long period of time, which doesn't make much sense in the context. We often say "I cut my hair short". You could also say "Yesterday I cut my hair drastically", a common expression which puts emphasis on the big change you talked about. You should use "We're going to" instead of "We will" when the plan already exists, you made the plan in the past. As you said "I'm going to my grandparents' house", the plan to have lunch with them is already made. "We'll" is more used for decisions or plans you're making at the time of speaking. Good job! :)