That's up to you to give up if you want to. Maybe this game was simply too complicated for you at this point in your "career" and you need to do a few smaller and less complex games first. I don't know, because I don't know you and what you have done in the past.
One thing occurs to me though. You could change the design around to fit what you are capable of doing. If you can't do the whole inventory, gem collection, etc... why don't you turn it into a simpler version of the same thing. Example, instead of having your game where you choose where to go, and can go back all the time, make it a sequence of levels, like many platform games. Also, you could make it where the gems don't give you anything, except maybe an extra life or something like that, and since the motivation isn't there, you don't have to worry about making sure the same thing can't be collected again.
Don't give up completely, and for sure don't erase your work, unless you are doing it with a re-writing purpose. If you can't do it now, put it up, and write out a text file for what you did, and what stopped you, and even my posts suggesting what to do. Then, when you get more experience, you can try again later, and having my suggestions there, you may suddenly understand what I was trying to say, and be able to implement it.
Anyway, good luck, whichever way you go with this.
I think I've got it! I tried making the room persistent, and when I exit the level and come back, the gems are gone!
I've added the bug fix in Spyro's parent object so when I enter the level portal, I don't go back to the exit level portal.