Correct, this does not qualify as a neder. One should say “bli shevua” rather than “bli neder”.
What you did was commit to something, which is a shevua. A neder would be if you were to prohibit yourself from something.
This was one of the first things my husband taught me when we met and I happened to use the phrase “bli neder”. It seems to be a little known fact in the frum community.