Question about fit for cycling shorts

OK.  First bicycle ride in years.  Rode about 5 miles.  That uphill climb on the way back was a killer!  Don't worry, I'm not giving up!

Second, my cycling shorts (new) are comfortable.  Not tight, but not baggy either.  I noticed on the ride back toward the end, the padding shifted forward.  Does this mean that they may be too big?  Or, just shifting around on the seat may have been the cause?  Any comments or suggestions would be helpful.