No, your first JEE Mains attempt won't be wasted even if you don't clear JEE Advanced or the second attempt of JEE Mains. The JEE Mains considers the best score from both attempts. So, if your first attempt was good, it will be considered for your overall rank. To appear for JEE Advanced, you need to qualify for JEE Mains only once in the same year. So, your first attempt qualifying score is enough to make you eligible for JEE Advanced.

I hope this information helps.