I have caulked the tub in the bathroom twice and both times the caulk is starting to peel. There is about a 1/4 inch gap between the tub and backsplash so the second time I filled in the gap with foam with no luck. Any suggestions on what I should do??

To be sure the caulking sticks you must remove the old, completely dry the area, then clean with alcohol to be sure there is no residue of any kind before applying the new caulk.
Use a hair dryer (on high) to dry the area thoroughly before cleaning with alcohol.
Also, be sure to give the new caulk plenty of time to dry before using the shower.