It is not permissible to use animals for target practice

Undoubtedly this action that you did is something which is forbidden according to sharee’ah and is not permitted. This is a form of tormenting animals which the Prophet (peace and blessings of Allaah be upon him) forbade. 

1.It was narrated in the hadeeth from ‘Abd-Allaah ibn ‘Umar that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “A woman was punished for a cat which she imprisoned until it died, and she entered Hell because of that. She did not feed it or give it water when she imprisoned it, and she did not leave it free to eat of the vermin of the earth.” (Narrated by al-Bukhaari, 2236; Muslim, 2242). Al-Nawawi said: the apparent meaning of the hadeeth is that she went to Hell only because of this sin.

2.It was narrated from Ibn ‘Umar (may Allaah be pleased with him) that he entered upon Yahyaa ibn Sa’eed and one of Yahyaa’s sons had tied up a hen and was shooting at it. Ibn ‘Umar walked over to him and untied it, then he brought it and the boy and said, “Do not allow your boys to tie up birds in order to kill them, for I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) forbidding the tying up of animals or other creatures in order to kill them.”

(Narrated by al-Bukhaari, 5195; Muslim, 1958. The version narrated by Muslim says, “The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed those who do that.”)

3.It says in another hadeeth which was narrated from Ibn ‘Abbaas that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do not use anything in which there is a soul as a target.” (Narrated by Muslim, 1957).

Al-Nawawi said: 

The Messenger of Allaah (peace and blessings of Allaah be upon him) forbade detaining or tying up animals (for the purpose of killing them); according to another report, ‘Do not take anything in which there is a soul as a target.’ The scholars said that tying up animals means restraining them whilst they are still alive in order to use them as targets and so on. The words ‘Do not take anything in which there is a soul as a target’ means do not use living animals as targets for shooting as targets made of leather and so on are used. This prohibition means that doing this is haraam. Hence the Prophet (peace and blessings of Allaah be upon him) said, according to the report narrated by Ibn ‘Umar which follows this report: “Allaah cursed the one who does that.” And because it is torturing animals, a waste of their [animals’] lives, a waste of money, causing the animal to die without slaughtering it in the proper Islamic manner if it is an animal whose meat may be eaten, and wasting an animal from which benefit may be derived in other ways if it is an animal whose meat may not be eaten. 

Sharh Muslim, 13/108 

You must repent sincerely to Allaah from this deed and seek His forgiveness, and do lots of good deeds so that Allaah will forgive your sin. 

And Allaah is the Guide to the straight path.