You get seats based on your KCET merit score so if that score is less, then you wont get a decent college. If you are talking about failing in boards, then if this happens then too you wont be able to  get into colleges through the KCET score. Because as per the KCET eligibility criteria, you need a minimum of aggregate 45% and above in your 12th boards to fulfill the criteria (for general category) and 40% and above for reserved category.

Refer to the site below for more information about the same...

https://engineering.careers360.com/articles/kcet-eligibility-criteria

Best wishes. Thank you.