I have over 100 W2-Gs but overall had a loss for the year. Is there a way in turbo tax to just enter the total for each casino rather than each W2-G?

Yes.  So long as the EIN of the payor is the same on all W-2G's, you can combine them and make a single entry.   You could also group them by EIN of the payor and enter one for each EIN number.