You are correct that both meanings are possible, but I think the second meaning will be inferred by the vast majority of recipients. This is because the first sentence establishes a setting in the future (next week) and this setting carries over to the next sentence.
It is easy to explicitly select one meaning or the other by adding to the statement:
A conditional sentence can use the future tense in the second clause:
If you study hard, you will pass the exam.
If I have time, I will visit him.
This is called by teachers, a conditional sentence, type 1 used for future, real situations or facts.
Teachers usually teach present unreal or future conditionals as given in the OP's examples:
If you didn'...
I was taught:
If I was - if the possibliity exists e.g. if I was a teacher (I'm not a teacher. But I could be one.)
If I were - if it's no real possibility e.g. if I were you (I'm not you. And I can impossibly be you.)
But I've met several times the opinion the two would be exchangeable. So, it can be that the strict distinction either gets generally ...