Will my credit be affected if the mortgage is in my dads name only but my name is on the deed, if the house is foreclosed on?

The mortgage company willl go after the borrower on record due to the fact that they lent the money to him based on his qualifications of purchasing the home. In regards to other forms of payments required on the home (i.e. taxes, insurance, etc.) it may be possible that you could be held liable as a co-owner of the home.

I would suggest that your best opportunity would be to see if you are able to Quit Claim off the property so your liability on the home is removed. Have you tried that yet?