Taiki.

It seems you didn’t understand how the verb finir is working.

First of all, your sentence is a shortcut. You would say “J’ai fini de lire le roman” to be more explicit. Using J’ai fini, without a verb after it, is a shortcut used a lot of time in french, and might be hard to understand by foreigners.

EDIT : After some research, shortcutting here is not a bad practice, but only something to be careful about to be understandable by foreigners.

Second, “finir” alone is used to signify “to finish”

“ça va mal finir” => this will end up badly.

Third, if you want to add the “end up” signification while using “finir”, you might say “j’ai fini par faire quelque chose” => I ended up doing something.

Hopefully, it is clear…

"Finir" carries the notion of "end". To finish something is to carry it to its end.

In French, the primary sense of the verb "finir" is a synonym to "terminer":

J’ai fini de préparer à manger, à table !

Je termine ma lecture et j’arrive !

The sense of "to end up" is "after the events, to be in a certain situation". In French if you want to use "finir" for that you have to use the right préposition:

Ils ont fini par me laisser passer.

J’ai fini avec un mal de crâne pas possible, et je me suis promis de ne plus jamais boire.

Or you can use another verb:

Je me suis retrouvé avec le roman entre les mains, alors que je n’en voulais pas.

In some unambiguous cases some parts of the sentence can be elided, and the result can seems strange for non-native speakers:

Après une bagarre de taverne, Grumsh finit (par se retrouver) à l’hôpital.

In case of doubt, try to insert "par se retrouver" (or "par me/te retrouver") after the verb "finir". If it makes more sense there is a good chance that there is an elision here and the meaning is "to end up".

Every word has a lot of possible meanings.

Among many meaning, « finir » can be translated to « To end up » or to « to complete ».

If « finir » is followed by an adjective (situation or a state), it means « to end up ».

for instance :
J’ai fini fauché -> I ended up broke;
J’ai fini fatigué -> I ended up tired.

If « finir » is followed by a noun or a verb, it means « to complete ».

for instance :
J’ai fini de cuisiner -> I completed cooking;
J’ai fini la révision de mes leçons -> I finished studying my lessons.