Here are a few suggestions I made. I'm not a native, so anyone is welcome to correct me. :)

Ils me faut marcher seul(e)
- I must walk alone
Faire face à la musique
- To face the music (Note: There is no "must" in this sentence, it is just a continuation of the first line, I think.)
De ce parcours que j'ai choisi,
- Of this course/path/route I've chosen
Le travail d'une vie.
- The work of a lifetime (Note: The word "entire" is not present, just "life" - "lifetime" flows a bit better in English though, I think.)
Mais quelque fois quand j'en ai assez,
- But sometimes when I've had enough (Note: I think "I've had enough" translates a little better than "I'm tired of that," though both I think work fine.)
Que je songe à tout abandonner
- When I think of giving up everything (Note: "To give up" works, but "giving up" flows a little nicer in English.)
Tu veux que je sois ce que je suis.
- You want me to be what I am (Note: I'm tempted to use "You want that I were what I am," just to show that the singer is using the subjonctif here, but it doesn't work at all. How you have it is, I think, the only way a native English speaker would ever say it.)
Je fonce alors je vie.
- I keep on going, and so I live. (Note: "Foncer" can be a few different things, but considering the singer is unhappy, I think "to keep on going" or "to keep on keepin' on" or something like that would work. Also, "je vie" is "I live" - not "I feel great." The meaning behind this line is that the singer just keeps living the way she is, bears her burdens, and lives - but doesn't enjoy it.)

J'imagine une force invincible,
- I imagine an invicible force
La beauté d'un monde unie.
- The beauty of a united world
J'imagine que l'on peut voler,
- I imagine that we will fly (Note: I think "on" works as "we" in this case, but I'm not sure. I was taught that it's "one," but "we" works better.)
J'imagine de cette force une réalité.
- I dream a reality from this strength (Note: This is rather poetic license, I think. While "I imagine this force a reality" literally works, it doesn't make sense. I think the subject is placed at the end to give emphasis, meaning the actual lyric should be "J'imagine une réalité de cette force," which is "I imagine a reality from this force" or I think a better way to say it in English is "I dream a reality from this strength")

Ce moment important
- This important moment
Dont je rêve depuis toujours
- That I always dreamed of (Note: "Depuis toujours" is "since forever" - I want to say there is an English phrase that would fit that translation nicely, but "always" works as well.)
Marquera tout un changement
- It will mark everything a change (Note: You missed the verb "marquer" in your translation, "to mark." Also, this translation is awkward until you read the second line - then it flows together a little better.)
À cet unique parcours
- To this unique path
J'ai au fond de moi la certitude
- Inside I am certain of that (Note: A bit free of a translation, something more literal would be "I have certainty deep within me" or something, but both work.)
Que la terre entière m'ouvre les bras
- That the whole world opens its arms to me (Note: Your translation just said "opens the arms" - you must include the "m'" at the beginning - "to me" - and "the arms" sounds strange in English, I believe you can be liberal and say "its arms.")

Elle qui m'encourage du nord au sud
- The world that encourages me from north to south (Note: "The" is not needed for these directions in this case.)
Rien ne marrâtera .
- Nothing will stop me (Note: I assume the "ne" in this case refers to the "ne...pas" structure, reinforcing how absolutely nothing will stop... the world? me? There isn't a pronoun here, so I'm uncertain how best to translate this.)

J'imagine une force invincible
La beauté d'un monde unie
J'imagine que l'on peut voler
Ji'magine de cette force une réalité
J'imagine que le temps est né
- I imagine the time is born
D'être fier pour le monde entier.
- To be proud for the whole world
J'imagine que l'on volera
- I imagine that we will fly
J'imagine cette force nous ralliant toi et moi.
- I imagine this force rallying us, you and me (Note: Interesting wording, I would add in the "nous/we" as well as "you and me" just to keep it more faithful to the original - again though, it depends on how literal you want to be with your translation.)
J'imagine cette force nous ralliant toi et moi.

J'imagine, j'imagine, j'imagine
J'imagine le meilleur en moi.
- I imagine the best in me
J'imagine, j'imagine, j'imagine
J'imagine le meilleur en toi.
- I imagine the best in you