HI young trumpet player. First, you'll have a much easier time if you just memorize all of your major and minor scales. You need to be able to play them easily. So take your time, but work at it. Also, it would be great if you could just start practicing your church songs with out music. You'll need to know what key it's played in to start. Practice playing lots of familiar melodies without music. Your brain will begin to make connections which will carry over into church rehearsals. Practice must be a discovery process. You must never be afraid of making mistakes. Learning is always, (or at least should always) be messy.
The person who suggested that you record the songs at rehearsal had a great idea. That way you can go home and do all your discovering in private. When you start to get a bit better, you'll want to show off your progress. It's not about being great...it's about progress. Your mind works just fine. You do however need to kind of program it first. You do that be "wood shedding," which simply means whittling away at it until it starts to look, (sound) like something respectable. It's dirty work, but you HAVE to do it if you want to progress. So go for it. Take some chances, get messy, and make mistakes.
Dan D
Studio Musician (trumpet)