dstan35 let's be realistic for right now. It sounds like you are lucky to be on the team. While I don't understand the can't play third because of weight you said you were going to be cut from the team until you volunteered to be catcher. Then when you played catcher you didn't do so well due to the fact that you've never really caught before. Honestly, you're not going to see the field again this year. While it's nice you've done everything the coach has asked from you and volunteered to warm up pitchers the question is - have you really gotten any better since beginning of the year?
Right now you need to focus on getting a head start for making the team next year. Go have an honest / private conversation with the coach and tell him you don't expect to get on the field the rest of the year. But ask him what are the chances of making the team next year, which position do you have the best chance at making the team, ask if someone will stay after practice to get extra work in at that position and what it will take to get on the team next year.
Hopefully I'm wrong and you're more solid on making the team than what I'm reading from your post. But if I'm right then you need to work on improving skills for next year more than trying to get time this year when you're not ready.