If you enter into the Sacrament of Marriage, then married life is your vocation. If you enter into the Sacrament of Holy Orders, then the priesthood is your vocation. Simple as.
The only sin in refusing your vocation would be if you were explicitly called (i.e. had made it through 6 years of seminary, satisfied the bishop or superior of your order, and had been formally called to receive Holy Orders) and then ran away. Up until that point, you cannot know your vocation, you can only discern to the best of your ability.
As someone who went through this battle (and is now happily married with a baby on the way :D ) I can share what my spiritual director told me. His advice was not to think about discernment as like a game of 'Deal or No Deal' where God has a 'correct' box and you need to work out how to chose it. Whatever vocation you accept with joy is the one God wanted you to accept, and through the sacraments God will give you the grace to live that vocation.
I honestly believe I could have been a priest, and I'd probably have been ok at it, if a little miserable at times. If I'd chosen it joyfully, God would have done it. Instead, I chose to be married, and in so doing, God chose to give me the vocation of a married man (the laws of cause and effect kind of break down when dealing with the divine mysteries). If it wasn't a choice, then there wouldn't be any real love behind it, and love is the nature of the gift God wants us to give. I give that gift to Him through my wife, and I am thankful that I did, but it could equally have been otherwise. If there was no real choice in the matter, there would be no love either.
If, on the other hand, you are entering into marriage with the specific intent of running away from the priesthood, then the motivation is all wrong. In that case, you would be doing something foolish - luckily, however, God has anticipated this eventuality and created a failsafe to stop you from doing this - what is the failsafe? It isn't found in Canon Law, nor in the Church's Tradition. It's simply the fact that you'll be hard pressed to find a woman who wants to marry you if it's so obvious that you don't love them, and aren't cut out for marriage, but just want to run away from being celibate! Finding a woman who'll marry you isn't easy at the best of times.
Ask yourself which gift you would feel most joyful in giving to God in the long term. And don't worry.