So, just to clarify, you were on a website and saw a prompt about installing an app, and it was downloaded immediately onto your device rather than directing you to the App Store... is that accurate?
If so, your device may have been compromised, and deleting the app may not be sufficient to remove the effects. Any time you install something not from the App Store, there is a risk that that is malware. The only known iOS malware relies on methods like these, or requires the phone to be jailbroken in the first place. I cannot say whether the app you downloaded actually is malicious or not.
To be entirely sure you are safe, you should immediately restore your iPad to factory settings, without restoring from backup. For help with that, see:
Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support