boost is the amount of pressure the turbo is producing.. (more boost + more pressure = more bhp).. stock glanza's/gt's run around .4 of a bar of boost on low turbo and .65 of a bar of boost on high turbo.. if thats all the mods you have on the car and your not planning on doin much more with it for awhile i suggest you remove aftermarket fpr and replace with stock one or bring it to someone to set the fueling right..(its probably the reason your car is drinking petrol) if your planning on upping the boost keep it and get it set up properly.... do not exceed .8 of a bar of boost without supporting modifications as you will hit "fuel cut".. hitting fuel cut explains itself really.. the ecu cuts fuel to the engine which is not good for the engine.. to combat this you have 2 choices.
1. get a good aftermarket exhaust mainifold and decat..the stock manifold is 2 restrictive and can damage you engine as you up the boost...you already have an aftermarket fpr..adjustable actuator.. source an aftermarket ecu like blitz, jam etc.. with these ecu's you can safely raise your boost levels without worrying about fuel cut.. stock engines can handle 1.2 bar safely but if you want more boost you will need to forge your engine first as the stock internals wont cope with anything over 1.2 bar of boost. get your fueling sorted for this way
2. aftermarket manifold and decat, you already have an aftermarket fpr, adjustable actuator, fcd (fuel cut defencer). you will have to get the car setup on a rolling road to get your fueling sorted this way
option 2 is far cheaper but it depends on how deep your pockets are really..lol..
you can start with the basics for now and give the car a good service.. plugs, leads, oil change etc etc and may i suggest you buy yourself a boost gauge as your first modification.. very important with these cars to keep an eye on your boost levels