Hi Stacey, welcome to the forums!
I noticed that you are two years younger than my younger sister…I will try to answer you the way I would answer her.
First of all, what does your fiance think about your feelings? This could be a great example of how you two communicate and work out problems…
Secondly, I don’t think you are being the bad kind of selfish. Wanting to go to school, travel, hang with friends etc are all normal things to want to do at your age and before marriage. It is not sinful.
Depending on your fiance’s thoughts, I would say to extend your engagement. Absolutely nothing is wrong with waiting a bit to get married. If this is the man God has chosen for you then things will work out.
I would tell my sister to discuss this openly with her fiance and then come up with a plan they can both live with.
For instance, let’s say if you go to school you would finish in “X” years. Is he ok with waiting to get married? Plan to do a little travelling during school breaks.
I think that if you guys have a great God-centered relationship then you both can make this work out for the best. The last thing you should do is ignore what you are feeling and get married anyway. Whatever you guys decide to do you need to come to a decision together.
If he has a problem waiting (while knowing that you still want to get married to him and that you have a timeline in which to do it) then maybe you need to rethink the relationship.
A good man should be happy that his future wife is putting so much thought into getting ready to be a good spouse and not just jumping into marriage only to divorce him later because she feels like she “missed out”.
Everything I have said is only my opinion. Things may be completely different for you, but it’s really hard to give advice over the internet with so little background info. So please feel free to ask more questions etc. There are a lot of great people here who will have great advice!