Your prayer is valid and you do not have to repeat it; do not worry about the smell that you noticed so long as you did not feel anything coming out of you. You should not pay attention to the waswaas that comes to your mind and cast aside the doubts that cross your mind.
With regard to the hadeeth which says that a man complained to the Prophet (blessings and peace of Allah be upon him) that he felt something during the prayer, and asked whether he should stop praying, and he said: No, unless you hear a sound or notice a smell (narrated by al-Bukhaari, 20546; Muslim, 361), this has to do with one who feels something and is not sure whether it came out; this indicates that one should not do something that is due to waswaas, because the certainty of being in a state of purity cannot be affected by uncertainty or doubt.
Shaykh Ibn Baaz (may Allah have mercy on him) said:
The believer should not pay attention to this waswaas, because this will encourage the Shaytaan, and the Shaytaan is keen to spoil the good deeds of the sons of Adam, such as prayer and so on. What he must do is be aware of his tricks and whispers, put his trust in Allah, and assume that whatever happens of waswaas is from the Shaytaan, so that he will not pay any attention to it. Then if something comes out of him and he is certain of it, not uncertain, he should clean himself again (istinja') and repeat wudoo'. But so long as there is any uncertainty, even if it is slight, then he should not pay attention to that, and he should still believe that he is in a state of purity and ward off the whispers of the Shaytaan.
End quote from Majmoo Fataawa Ibn Baaz, 10/123
And Allah knows best.
Reproduced from Islam QA