adult size backpack (south sunnyvale)

this backpack feels too big for my body and straps slide off my shoulders. I was going to put another strap with clip to go across front of chest to keep should straps in place. but I recently got another backpack that works better for me. I can include the materials to add that across chest strap incl clip. brand is Bag Nation. has one big compartment and many very useful additional ones around sides and front. well made and attractive. I did one repair around zipper where it was disattaching from backpack itself.