I majored in exercise phys in college and am "certified to weight train". I will reiterate what Charlie has said and say there is some GREAT and TRUTHFUL information already provided. I will also add that these are not the only ways you can obtain your goal.
Remember that Rome was not built in a day. People who want to bench #300 and the person who wants to draw #80 all have the same need, to train their muscles on a consistent basis over an extended period of time.
Some things to remember, weight gains do not typically happen over night. From my experience(training people) it usually takes at least 2 weeks to see a little gain(10 or so pounds) while benching, though individual results will vary.
I would do do a variety of tactics to help obtain this goal..
START SLOW.
(Majority of injuries occur when muscles are trained for the movement being done.)
draw until it begins to get uncomfortable, hold a few seconds, and let down(REPEAT). BE SURE YOU DON'T JUST LET THE BOW STRING DOWN QUICKLY, SLOWLY CONTROL THE LET DOWN. In weight lifting, they call this a "negative rep" and is debatably just as, if not more important than the positive rep. Do 5 or so reps of this remembering to take it easy and not tear something starting off.
BE CONSISTENT!
- be sure that you maintain your 3 days a week etc. Majority of people quit after 10 or so days because they don't see the results they want. Majority of goals that are worth reaching take time and effort, this is no different.
KEEP YOUR EYES ON THE PRIZE
- just keep at it and in a month or so i would bet you will be a lot closer to the goal you have set.
Keep us updated.
Good luck,
Daniel