Both are correct.
"να αγοράζω" is continuous form.
ex: Μου αρέσει να αγοράζω ρούχα. I like buying clothes.
"να αγοράσω" is simple (not continuous) form.
ex: Θέλω να αγοράσω ένα καπέλο. I want to buy a hat.
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.