I need tips on calories?

Before you ask the legal age to drink were I am is 18 my age! OK so lately I have been healthy eating, and I got invited to one of my close friends party's. Only I'm scared that once I start drinking I will go back to my rubbish eating habits. I have to go though cause she is a close friend. Do you think one day will mess up plans I have been exercising regularly too. I was thinking since there are a lot of calories in drink and I don't want to over my limit I should skip my dinner? Then I wouldn't feel guilty about taking in too many? Any advice sorry this is long.
I need tips on calories?
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