Did I make a mistake? Is it possible that I don't have enough gum surface for the denture? (Photo)

49 y/o, 2 weeks post for immediate denture upper only. Denture does not fit, feels very bulky and I have a lisp. There is about 1/2 inch space between my actual gum and the denture causing the appearance of a huge over bite. When I smile my lips get lost in the open space of the denture and gum. Is it possible that I don't have enough gum surface for the denture? What other options can I research? I thought I was on the road to fixing a long overdue issue but it seems worst than before. Please Help

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