well the issues are a bit obvious ..i will try to explain so you can use the comment for the next time
first the selections are very choppy , jagged , try to work with different feather settings , maybe choose 0,2 for the main selections (instead of 0)
you can set this in the box above
then you rebrushed the bike but why are the dimensions and proportions changed ?
the rear wheel looks like the bike has been in a accident (best way to describe)
its off now
the front whel has got the same issue , also lack of shading (like on the front fender) makes it toutch the tyre
you should <if you dont change stuff and keep the bike as it> is work like this :
make sure the size is at least 2000x... pix or bigger , great quality (because its a re-brush and your a beginner so that works best)
then really zoom in so you can still see what you do but everything is clear
then take time on selections , one of the most important things
best is to master the pentool , i myslf never use that and my hand and eye are so steady i can work with the polygonal tool (also use the eliptoical tool a lot)
but thats just your own choice
most people when mastering the pen tool will get the best results
take a good look at the light area's and dark area's
you could keep a master pic and when you brushed a peice look at the master for guidence to where the lighter area's and darker aerea's should be
basicly this re-brushing is painstaking boring work where you will only get a great result when you really hang in there and take the time
hope its usefull for you ?