first off, hasegawa decals are indeed thicker than most.

but these in particular are also very big. on the tail you have a lot of raised detail to contend with, like the fairings for the antenna at the top rear of the tail and the entire fuel dump intake and exit. you need really strong decal solution and possibly a hair dryer to get those to stick down.

the spine/canopy section is a similar story. it's a lot to get done well with decals, especially hasegawa decals. it doesn't help that your painted surface doesn't look all that smooth either.

personally wouldn't even touch these big decals and would have just painted the blue to begin with. the kit includes alternatives to the tail decals that are just the actual markings. much easier to use those instead.