Defining Basic Services?

I recently completed a gig that paid well for what I consider to be my basic services. I.E. session, prelim edits, proofs posted, images selected for further edits, provide images. However, this particular client ended up requesting quite a bit more editing and processing: three different rounds of revisions, more involved edits, etc.

I didn't feel comfortable coming back asking for more money since I didn't exactly define clearly what my services were. So I did perhaps 4 additional hours of editing without additional fee. I realize this is my mistake but not sure how to address it for future projects. Is it simply a matter of defining these issues in the contract? Basically spelling out what is included for the negotiated fee and any additional work will require additional fees? Or should I just negotiate a fee that covers me regardless and if the edits required are less on a particular job, I just have more profit built in?

I am admittedly just starting out and even though I am happy to making decent money at this part time, I want to find ways to avoid this situation in the future. Any thoughts?

You are correct. State what your base shoot rate includes and then define what the extras are, in detail, and place a price to each. I say "in detail" because a basic edit to me and you may not be as extensive as what the client is expecting. Spell out what a basic edit is and what a more involved edit is and what that would involve.