I run Gimp 2.8.18 in a netbook same size, running Bodhi linux no problem The basics for any:
1. You do not need all the tools showing. Edit -> Preferences -> Toolbox and untick the ones you will never use.
They are always avavilable from the tools menu or a right click on the canvas.
2. Adjust the width of the docks. This is the one that is possibly stopping your resizing the whole gimp window. Make the toolbox and tool options side wider. There are hotspots to click and drag on the edges.
3. Got a dialog that is too long and off the screen. Alt-click and drag to get to the ok button.
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When you have it set up, remember to use Edit -> Preferences -> Window Management. Un-tick save window positions on exit. Click on save window positions now.
edit: This is my Bodhi linux netbook, a screenshot of the desktop inside of Gimp on the desktop

almost a droste. If you have a menu bar or systems tray that can autohide, might be worth invoking that, but not absolutely necessary.
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