I think we all have had these type of disappointments when customizing our toys when we were young. The experiences are what eventually makes us into better modelers as we grow older.
If you just used regular masking tape (tan) then that could be the problem as the inexpensive stuff never was meant for crisp detail lines. The important thing to know is not to rely on the tape so much where you are painting and stay away from slathering it on. You still need to take your time and try to follow the edges without loading it up with a lot paint. The other thing that I have found is that paint pens often gob too much paint on. I have tons of pens and use them for specific areas but would not use them on larger areas or where they come in contact with tape because of the lack of flow control. Using a brush with light coats might have had better results. The better way may have been to disassemble the train, mask off all areas not to be painted, use a smooth piece of flat plastic, ice cream stick or toothpick to smooth out the edges of the masking tape to help the pressure sensitive glue to adhere to your project. Then use a spray paint in several very light coats. Of course the optimum way is to use an Airbrush but not everyone has access to one. I only use this tape (no copy cats) in the 1" size for modeling as the edge adhesion is great, peels off easy without pulling paint off underneath and leaves no glue residue, its also soft and pliable. One roll should last you into your adult life. http://www.scotchblue.com/wps/portal/3M/...207&rt=rud Get the one with the gold lettering on it and not their regular, plain, blue painters tape.
To repair what you have, could you now just use a small brush a color paint similar to where the bleed through occurred and touch up the troubled area?
If you just used regular masking tape (tan) then that could be the problem as the inexpensive stuff never was meant for crisp detail lines. The important thing to know is not to rely on the tape so much where you are painting and stay away from slathering it on. You still need to take your time and try to follow the edges without loading it up with a lot paint. The other thing that I have found is that paint pens often gob too much paint on. I have tons of pens and use them for specific areas but would not use them on larger areas or where they come in contact with tape because of the lack of flow control. Using a brush with light coats might have had better results. The better way may have been to disassemble the train, mask off all areas not to be painted, use a smooth piece of flat plastic, ice cream stick or toothpick to smooth out the edges of the masking tape to help the pressure sensitive glue to adhere to your project. Then use a spray paint in several very light coats. Of course the optimum way is to use an Airbrush but not everyone has access to one. I only use this tape (no copy cats) in the 1" size for modeling as the edge adhesion is great, peels off easy without pulling paint off underneath and leaves no glue residue, its also soft and pliable. One roll should last you into your adult life. http://www.scotchblue.com/wps/portal/3M/...207&rt=rud Get the one with the gold lettering on it and not their regular, plain, blue painters tape.
To repair what you have, could you now just use a small brush a color paint similar to where the bleed through occurred and touch up the troubled area?