There are many good points and correct responses (why dwell on what is or may be technically incorrect or other wise?), but let's consider the reality in the context of your circumstances.
[1] You are newly certified (me too). This means that youre probably not that experienced (unless youve been logging quite a few dives in the frigid waters of the winter). Also consider the experience and common sense youve acquired in your dive training. Are your reactions to problem situations quick and correct? Be honest. How likely are you to place your, or worse yet your buddies, life in danger if the unfortunate happened? Having a dive master near by may be the answer, but only if he/she can act as a 3rd buddy. Find out in advance if this will be the case. If so, be prepared to pay that person for the privilege to learn more and feel safer at the same time.
[2] This is a vacation (bought and paid for I assume). So you really may not be able to undo your plans (not without severe financial repercussions anyway). So make the best of it. Solve the issues before you leave. What about going back to you LDS where you got your training and see what they can do to help you prepare. I went to the pool every weekend durring the 5 weeks of my OW training, for 2-3 hours each day, focused soley upon perfecting the techniques so that I could perform them as nearly perfectly as was possible in the placid, safe harbour of the pool (knowing that there was a greater element of unfamiliarity and risk in the OW). Have your dive instructor speak with the dive master where you plan to vacation better yet, have him/her write you a letter of recommendation commenting on your skills and what they feel is appropriate for you to tackle. Who says you have to do both dives? Can you dive the reef twice (did you ask)?
[3] Best rule-of-thumb: Dont make any dive you are not absolutely sure that you are prepared for unless you are assisted by an instructor or dive master. Even then, if you dont feel that they have your best interest at heart dont dive with them either. Remember how much emphasis was placed on planning your dive in your OW class (I hope anyway)? There is a good reason that this time was taken and the emphasis was great and serious. Dont lose sight of that important point Plan your dive (thoroughly) and dive your plan (dont deviate from the plan). This I know is 100% sure every time: If you are not sure that you can do it you probably shouldnt try it unless failure is an option. If failure is not an option practice, practice, practice until you know you can!
Now whatever you do - have fun and have it safely!
:newbie: