Please show a screenshot of layer view to show the problem. There are several reasons - the most common are:
walls too thin
parts not manifold
Showing a picture will help me realize your particular issue but know that this is a common problem and easy to fix.
Firstly preview your print in Cura to see if Cura is not printing the whole file. Next get the latest version of Cura and preview in that. If Cura is not showing the full print then upload your file and Cura settings here. If Cura is showing the full print then maybe you are having an extrusion problem. Let us know how you go and maybe upload a pic of your print here first.
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